Interventions to prevent occupational noise‐induced hearing loss

Comparison 1. Legislation to decrease noise exposure (long‐term) ‐ ITS

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 Immediate change in level Show forest plot	1		immediate change in level (Random, 95% CI)	Totals not selected
Open in figure viewer Analysis 1.1 Comparison 1 Legislation to decrease noise exposure (long‐term) ‐ ITS, Outcome 1 Immediate change in level.
1.1 Surface noise Intervention (Int) Year 1999	1		immediate change in level (Random, 95% CI)	0.0 [0.0, 0.0]
1.2 Underground noise Int Year 1999	1		immediate change in level (Random, 95% CI)	0.0 [0.0, 0.0]
1.3 Surface noise Int Year 2000	1		immediate change in level (Random, 95% CI)	0.0 [0.0, 0.0]
1.4 Underground noise Int Year 2000	1		immediate change in level (Random, 95% CI)	0.0 [0.0, 0.0]
2 Change in slope Show forest plot	1		change in slope (Random, 95% CI)	Totals not selected
Open in figure viewer Analysis 1.2 Comparison 1 Legislation to decrease noise exposure (long‐term) ‐ ITS, Outcome 2 Change in slope.
2.1 Surface noise Int Year 1999	1		change in slope (Random, 95% CI)	0.0 [0.0, 0.0]
2.2 Underground noise Int Year 1999	1		change in slope (Random, 95% CI)	0.0 [0.0, 0.0]
2.3 Surface noise Int Year 2000	1		change in slope (Random, 95% CI)	0.0 [0.0, 0.0]
2.4 Underground noise Int Year 2000	1		change in slope (Random, 95% CI)	0.0 [0.0, 0.0]

Comparison 2. HPD (muffs) with instructions vs without instructions (immediate) ‐ RCT

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 Noise attenuation at 0.5 kHz (REAT) Show forest plot	1	40	Mean Difference (IV, Random, 95% CI)	2.34 [‐0.85, 5.54]
Open in figure viewer Analysis 2.1 Comparison 2 HPD (muffs) with instructions vs without instructions (immediate) ‐ RCT, Outcome 1 Noise attenuation at 0.5 kHz (REAT).
1.1 Wilson Sound Ban cap	1	20	Mean Difference (IV, Random, 95% CI)	4.1 [‐2.47, 10.67]
1.2 Bilsom UF‐1 muff	1	20	Mean Difference (IV, Random, 95% CI)	1.80 [‐1.86, 5.46]
2 Noise attenuation at 1 kHz (REAT) Show forest plot	1	40	Mean Difference (IV, Random, 95% CI)	0.89 [‐3.02, 4.80]
Open in figure viewer Analysis 2.2 Comparison 2 HPD (muffs) with instructions vs without instructions (immediate) ‐ RCT, Outcome 2 Noise attenuation at 1 kHz (REAT).
2.1 Wilson Sound Ban Cap	1	20	Mean Difference (IV, Random, 95% CI)	3.80 [‐3.70, 11.30]
2.2 Bilsom UF‐1 Muff	1	20	Mean Difference (IV, Random, 95% CI)	‐0.20 [‐4.78, 4.38]
3 Noise attenuation at 2 kHz (REAT) Show forest plot	1	40	Mean Difference (IV, Random, 95% CI)	2.57 [‐0.23, 5.38]
Open in figure viewer Analysis 2.3 Comparison 2 HPD (muffs) with instructions vs without instructions (immediate) ‐ RCT, Outcome 3 Noise attenuation at 2 kHz (REAT).
3.1 Wilson Sound Ban Cap	1	20	Mean Difference (IV, Random, 95% CI)	2.70 [‐1.89, 7.29]
3.2 Bilsom UF‐1 Muff	1	20	Mean Difference (IV, Random, 95% CI)	2.5 [‐1.05, 6.05]
4 Noise attenuation at 3 kHz (REAT) Show forest plot	1	40	Mean Difference (IV, Random, 95% CI)	2.23 [0.09, 4.36]
Open in figure viewer Analysis 2.4 Comparison 2 HPD (muffs) with instructions vs without instructions (immediate) ‐ RCT, Outcome 4 Noise attenuation at 3 kHz (REAT).
4.1 Wilson Sound Ban Cap	1	20	Mean Difference (IV, Random, 95% CI)	1.60 [‐3.01, 6.21]
4.2 Bilsom UF‐1 Muff	1	20	Mean Difference (IV, Random, 95% CI)	2.40 [‐0.01, 4.81]
5 Noise attenuation at 4 kHz (REAT) Show forest plot	1	40	Mean Difference (IV, Random, 95% CI)	0.83 [‐3.28, 4.95]
Open in figure viewer Analysis 2.5 Comparison 2 HPD (muffs) with instructions vs without instructions (immediate) ‐ RCT, Outcome 5 Noise attenuation at 4 kHz (REAT).
5.1 Wilson Sound Ban Cap	1	20	Mean Difference (IV, Random, 95% CI)	0.90 [‐6.18, 7.98]
5.2 Bilsom UF‐1 Muff	1	20	Mean Difference (IV, Random, 95% CI)	0.80 [‐4.26, 5.86]
6 Noise attenuation at 6 kHz (REAT) Show forest plot	1	40	Mean Difference (IV, Random, 95% CI)	0.64 [‐3.76, 5.04]
Open in figure viewer Analysis 2.6 Comparison 2 HPD (muffs) with instructions vs without instructions (immediate) ‐ RCT, Outcome 6 Noise attenuation at 6 kHz (REAT).
6.1 Wilson Sound Ban Cap	1	20	Mean Difference (IV, Random, 95% CI)	2.30 [‐7.31, 11.91]
6.2 Bilsom UF‐1 Muff	1	20	Mean Difference (IV, Random, 95% CI)	0.20 [‐4.75, 5.15]
7 Noise attenuation at 8 kHz (REAT) Show forest plot	1	40	Mean Difference (IV, Random, 95% CI)	1.14 [‐3.59, 5.87]
Open in figure viewer Analysis 2.7 Comparison 2 HPD (muffs) with instructions vs without instructions (immediate) ‐ RCT, Outcome 7 Noise attenuation at 8 kHz (REAT).
7.1 Wilson Sound Ban Cap	1	20	Mean Difference (IV, Random, 95% CI)	2.0 [‐8.13, 12.13]
7.2 Bilsom UF‐1 Muff	1	20	Mean Difference (IV, Random, 95% CI)	0.90 [‐4.45, 6.25]

Comparison 3. HPD (plugs) with instructions vs without instructions (immediate) ‐ RCT

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 Noise attenuation at 0.5 kHz (REAT) Show forest plot	1	40	Mean Difference (IV, Random, 95% CI)	12.69 [7.69, 17.69]
Open in figure viewer Analysis 3.1 Comparison 3 HPD (plugs) with instructions vs without instructions (immediate) ‐ RCT, Outcome 1 Noise attenuation at 0.5 kHz (REAT).
1.1 EAR foam plugs	1	20	Mean Difference (IV, Random, 95% CI)	16.30 [5.93, 26.67]
1.2 UltraFit plugs	1	20	Mean Difference (IV, Random, 95% CI)	11.6 [5.89, 17.31]
2 Noise attenuation at 1 kHz (REAT) Show forest plot	1	40	Mean Difference (IV, Random, 95% CI)	13.31 [8.13, 18.50]
Open in figure viewer Analysis 3.2 Comparison 3 HPD (plugs) with instructions vs without instructions (immediate) ‐ RCT, Outcome 2 Noise attenuation at 1 kHz (REAT).
2.1 EAR foam plugs	1	20	Mean Difference (IV, Random, 95% CI)	15.40 [5.62, 25.18]
2.2 UltraFit plugs	1	20	Mean Difference (IV, Random, 95% CI)	12.5 [6.39, 18.61]
3 Noise attenuation at 2 kHz (REAT) Show forest plot	1	40	Mean Difference (IV, Random, 95% CI)	9.62 [4.52, 14.72]
Open in figure viewer Analysis 3.3 Comparison 3 HPD (plugs) with instructions vs without instructions (immediate) ‐ RCT, Outcome 3 Noise attenuation at 2 kHz (REAT).
3.1 EAR foam plugs	1	20	Mean Difference (IV, Random, 95% CI)	7.90 [‐1.21, 17.01]
3.2 UltraFit plugs	1	20	Mean Difference (IV, Random, 95% CI)	10.40 [4.25, 16.55]
4 Noise attenuation at 3 kHz (REAT) Show forest plot	1	40	Mean Difference (IV, Random, 95% CI)	6.71 [2.66, 10.76]
Open in figure viewer Analysis 3.4 Comparison 3 HPD (plugs) with instructions vs without instructions (immediate) ‐ RCT, Outcome 4 Noise attenuation at 3 kHz (REAT).
4.1 EAR foam plugs	1	20	Mean Difference (IV, Random, 95% CI)	6.20 [‐1.54, 13.94]
4.2 UltraFit plugs	1	20	Mean Difference (IV, Random, 95% CI)	6.90 [2.15, 11.65]
5 Noise attenuation at 4 kHz (REAT) Show forest plot	1	40	Mean Difference (IV, Random, 95% CI)	7.97 [3.60, 12.34]
Open in figure viewer Analysis 3.5 Comparison 3 HPD (plugs) with instructions vs without instructions (immediate) ‐ RCT, Outcome 5 Noise attenuation at 4 kHz (REAT).
5.1 EAR foam plugs	1	20	Mean Difference (IV, Random, 95% CI)	6.00 [‐1.23, 13.23]
5.2 UltraFit plugs	1	20	Mean Difference (IV, Random, 95% CI)	9.10 [3.62, 14.58]
6 Noise attenuation at 6 kHz (REAT) Show forest plot	1	40	Mean Difference (IV, Random, 95% CI)	12.13 [6.21, 18.05]
Open in figure viewer Analysis 3.6 Comparison 3 HPD (plugs) with instructions vs without instructions (immediate) ‐ RCT, Outcome 6 Noise attenuation at 6 kHz (REAT).
6.1 EAR foam plugs	1	20	Mean Difference (IV, Random, 95% CI)	9.2 [‐1.87, 20.27]
6.2 UltraFit plugs	1	20	Mean Difference (IV, Random, 95% CI)	13.3 [6.30, 20.30]
7 Noise attenuation at 8 kHz (REAT) Show forest plot	1	40	Mean Difference (IV, Random, 95% CI)	11.07 [4.51, 17.64]
Open in figure viewer Analysis 3.7 Comparison 3 HPD (plugs) with instructions vs without instructions (immediate) ‐ RCT, Outcome 7 Noise attenuation at 8 kHz (REAT).
7.1 EAR foam plugs	1	20	Mean Difference (IV, Random, 95% CI)	7.60 [‐0.97, 16.17]
7.2 UltraFit plugs	1	20	Mean Difference (IV, Random, 95% CI)	14.3 [6.11, 22.49]
8 Mean noise attenuation over 0.5, 1, 2, 3, 4, 6, 8 kHz (REAT) Show forest plot	2	140	Mean Difference (IV, Fixed, 95% CI)	8.59 [6.92, 10.25]
Open in figure viewer Analysis 3.8 Comparison 3 HPD (plugs) with instructions vs without instructions (immediate) ‐ RCT, Outcome 8 Mean noise attenuation over 0.5, 1, 2, 3, 4, 6, 8 kHz (REAT).
8.1 Moldex Comets, EN352, USA	1	100	Mean Difference (IV, Fixed, 95% CI)	8.34 [6.58, 10.10]
8.2 EAR foam plugs	1	20	Mean Difference (IV, Fixed, 95% CI)	9.8 [0.60, 19.00]
8.3 UltraFit plugs	1	20	Mean Difference (IV, Fixed, 95% CI)	11.16 [4.87, 17.45]

Comparison 4. HPD (plugs) lower noise reduction rate (NRR) with instructions vs higher NRR without instructions (immediate) ‐ RCT

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 Mean attenuation at 0.5, 1, 2, 3, 4, 6, 8 kHz Show forest plot	1		Mean Difference (IV, Fixed, 95% CI)	Subtotals only
Open in figure viewer Analysis 4.1 Comparison 4 HPD (plugs) lower noise reduction rate (NRR) with instructions vs higher NRR without instructions (immediate) ‐ RCT, Outcome 1 Mean attenuation at 0.5, 1, 2, 3, 4, 6, 8 kHz.
1.1 NRR 20 vs NRR 30	1	100	Mean Difference (IV, Fixed, 95% CI)	2.62 [1.75, 3.49]

Comparison 5. HPD with ANC vs without ANC (immediate)

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 Noise attenuation (dB) Show forest plot	1	4	Mean Difference (IV, Fixed, 95% CI)	0.0 [0.0, 0.0]
Open in figure viewer Analysis 5.1 Comparison 5 HPD with ANC vs without ANC (immediate), Outcome 1 Noise attenuation (dB).
1.1 Alpha‐200 series with Active Noise Cancelling	1	2	Mean Difference (IV, Fixed, 95% CI)	0.0 [0.0, 0.0]
1.2 Gentex/Bose Active Noise Cancelling	1	2	Mean Difference (IV, Fixed, 95% CI)	0.0 [0.0, 0.0]
2 TTS at 1 kHz (before exposure ‐ after exposure ) Show forest plot	1		Mean Difference (IV, Random, 95% CI)	Subtotals only
Open in figure viewer Analysis 5.2 Comparison 5 HPD with ANC vs without ANC (immediate), Outcome 2 TTS at 1 kHz (before exposure ‐ after exposure ).
3 TTS at 2 kHz (before exposure ‐ after exposure ) Show forest plot	1		Mean Difference (IV, Random, 95% CI)	Subtotals only
Open in figure viewer Analysis 5.3 Comparison 5 HPD with ANC vs without ANC (immediate), Outcome 3 TTS at 2 kHz (before exposure ‐ after exposure ).
4 TTS at 4 kHz (before exposure ‐ after exposure ) Show forest plot	1		Mean Difference (IV, Random, 95% CI)	Subtotals only
Open in figure viewer Analysis 5.4 Comparison 5 HPD with ANC vs without ANC (immediate), Outcome 4 TTS at 4 kHz (before exposure ‐ after exposure ).
5 TTS at 6 kHz (before exposure ‐ after exposure ) Show forest plot	1		Mean Difference (IV, Random, 95% CI)	Subtotals only
Open in figure viewer Analysis 5.5 Comparison 5 HPD with ANC vs without ANC (immediate), Outcome 5 TTS at 6 kHz (before exposure ‐ after exposure ).
6 TTS at 8 kHz (before exposure ‐ after exposure ) Show forest plot	1		Mean Difference (IV, Random, 95% CI)	Subtotals only
Open in figure viewer Analysis 5.6 Comparison 5 HPD with ANC vs without ANC (immediate), Outcome 6 TTS at 8 kHz (before exposure ‐ after exposure ).

Comparison 6. Custom‐moulded musician HPD (plugs) with higher versus HPD (plugs) with lower noise attenuation

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 Noise attenuation dB(A) Show forest plot	1	20	Mean Difference (IV, Random, 95% CI)	3.10 [1.12, 5.08]
Open in figure viewer Analysis 6.1 Comparison 6 Custom‐moulded musician HPD (plugs) with higher versus HPD (plugs) with lower noise attenuation, Outcome 1 Noise attenuation dB(A).

Comparison 7. HPD (various) noise attenuation (immediate)

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 Noise attenuation (dB) Show forest plot	1	36	Mean Difference (IV, Fixed, 95% CI)	0.0 [0.0, 0.0]
Open in figure viewer Analysis 7.1 Comparison 7 HPD (various) noise attenuation (immediate), Outcome 1 Noise attenuation (dB).
1.1 Peltor H61 Muff Elec	1	6	Mean Difference (IV, Fixed, 95% CI)	0.0 [0.0, 0.0]
1.2 Peltor H7 Muff Elec	1	6	Mean Difference (IV, Fixed, 95% CI)	0.0 [0.0, 0.0]
1.3 Peltor H6 Muff Elec	1	6	Mean Difference (IV, Fixed, 95% CI)	0.0 [0.0, 0.0]
1.4 Bilsom Marksman Muff Elec	1	6	Mean Difference (IV, Fixed, 95% CI)	0.0 [0.0, 0.0]
1.5 Silenta Hunter Muff Elec	1	6	Mean Difference (IV, Fixed, 95% CI)	0.0 [0.0, 0.0]
1.6 EAR Ultra 9000 Plug	1	6	Mean Difference (IV, Fixed, 95% CI)	0.0 [0.0, 0.0]

Comparison 8. HLPP with noise level indicator vs no noise level indicator

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 Change in noise levels at 2 months' follow‐up Show forest plot	1	132	Mean Difference (IV, Random, 95% CI)	0.32 [‐2.44, 3.08]
Open in figure viewer Analysis 8.1 Comparison 8 HLPP with noise level indicator vs no noise level indicator, Outcome 1 Change in noise levels at 2 months' follow‐up.
1.1 Extensive information plus NLI vs information only	1	64	Mean Difference (IV, Random, 95% CI)	‐0.40 [‐4.37, 3.57]
1.2 Information plus NLI vs Information only	1	68	Mean Difference (IV, Random, 95% CI)	1.0 [‐2.84, 4.84]
2 Change in noise levels at 4 months' follow‐up Show forest plot	1	132	Mean Difference (IV, Fixed, 95% CI)	‐0.14 [‐2.66, 2.38]
Open in figure viewer Analysis 8.2 Comparison 8 HLPP with noise level indicator vs no noise level indicator, Outcome 2 Change in noise levels at 4 months' follow‐up.
2.1 Extensive information plus NLI vs information only	1	64	Mean Difference (IV, Fixed, 95% CI)	‐0.30 [‐3.95, 3.35]
2.2 Information plus NLI vs information only	1	68	Mean Difference (IV, Fixed, 95% CI)	0.0 [‐3.48, 3.48]

Comparison 9. HLPP with extensive information vs information only

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 Change in noise levels at 2 months' follow‐up Show forest plot	1		Mean Difference (IV, Fixed, 95% CI)	Totals not selected
Open in figure viewer Analysis 9.1 Comparison 9 HLPP with extensive information vs information only, Outcome 1 Change in noise levels at 2 months' follow‐up.
2 Change in noise levels at 4 months' follow‐up Show forest plot	1		Mean Difference (IV, Random, 95% CI)	Totals not selected
Open in figure viewer Analysis 9.2 Comparison 9 HLPP with extensive information vs information only, Outcome 2 Change in noise levels at 4 months' follow‐up.

Comparison 10. V‐51‐R plug versus EAR plug (immediate)

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 TTS at 0.5 kHz (Hearing loss before exposure ‐ after exposure ) Show forest plot	1	70	Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]
Open in figure viewer Analysis 10.1 Comparison 10 V‐51‐R plug versus EAR plug (immediate), Outcome 1 TTS at 0.5 kHz (Hearing loss before exposure ‐ after exposure ).
1.1 After 8 minutes out of noise	1	18	Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]
1.2 After 14.6 minutes out of noise	1	18	Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]
1.3 After 20 minutes out of noise	1	17	Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]
1.4 After 27.2 minutes out of noise	1	17	Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]
2 TTS at 1 kHz (before exposure ‐ after exposure ) Show forest plot	1		Mean Difference (IV, Random, 95% CI)	Subtotals only
Open in figure viewer Analysis 10.2 Comparison 10 V‐51‐R plug versus EAR plug (immediate), Outcome 2 TTS at 1 kHz (before exposure ‐ after exposure ).
2.1 After 8 minutes out of noise	1	18	Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]
2.2 After 14.6 minutes out of noise	1	18	Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]
2.3 After 20 minutes out of noise	1	17	Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]
2.4 After 27.2 minutes out of noise	1	17	Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]
3 TTS at 2 kHz (before exposure ‐ after exposure ) Show forest plot	1		Mean Difference (IV, Random, 95% CI)	Subtotals only
Open in figure viewer Analysis 10.3 Comparison 10 V‐51‐R plug versus EAR plug (immediate), Outcome 3 TTS at 2 kHz (before exposure ‐ after exposure ).
3.1 After 8 minutes out of noise	1	18	Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]
3.2 After 14.6 minutes out of noise	1	18	Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]
3.3 After 20 minutes out of noise	1	17	Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]
3.4 After 27.2 minutes out of noise	1	17	Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]
4 TTS at 3 kHz (before exposure ‐ after exposure ) Show forest plot	1		Mean Difference (IV, Random, 95% CI)	Subtotals only
Open in figure viewer Analysis 10.4 Comparison 10 V‐51‐R plug versus EAR plug (immediate), Outcome 4 TTS at 3 kHz (before exposure ‐ after exposure ).
4.1 After 8 minutes out of noise	1	18	Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]
4.2 After 14.6 minutes out of noise	1	18	Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]
4.3 After 20 minutes out of noise	1	17	Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]
4.4 After 27.2 minutes out of noise	1	17	Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]
5 TTS at 4 kHz (before exposure ‐ after exposure) Show forest plot	1		Mean Difference (IV, Random, 95% CI)	Subtotals only
Open in figure viewer Analysis 10.5 Comparison 10 V‐51‐R plug versus EAR plug (immediate), Outcome 5 TTS at 4 kHz (before exposure ‐ after exposure).
5.1 After 8 minutes out of noise	1	18	Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]
5.2 After 14.6 minutes out of noise	1	18	Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]
5.3 After 20 minutes out of noise	1	17	Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]
5.4 After 27.2 minutes out of noise	1	17	Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]
6 TTS at 6 kHz (before exposure ‐ after exposure) Show forest plot	1		Mean Difference (IV, Random, 95% CI)	Subtotals only
Open in figure viewer Analysis 10.6 Comparison 10 V‐51‐R plug versus EAR plug (immediate), Outcome 6 TTS at 6 kHz (before exposure ‐ after exposure).
6.1 After 8 minutes out of noise	1	18	Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]
6.2 After 14.6 minutes out of noise	1	18	Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]
6.3 After 20 minutes out of noise	1	17	Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]
6.4 After 27.2 minutes out of noise	1	17	Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]

Comparison 11. Earmuffs vs earplugs (long‐term)

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 Hearing loss change over 3 years (4 kHz / STS) Show forest plot	2		OR (Random, 95% CI)	Subtotals only
Open in figure viewer Analysis 11.1 Comparison 11 Earmuffs vs earplugs (long‐term), Outcome 1 Hearing loss change over 3 years (4 kHz / STS).
1.1 High noise exposure > 89 dB(A)	2		OR (Random, 95% CI)	0.80 [0.63, 1.03]
1.2 Low noise exposure < 89 dB(A)	2		OR (Random, 95% CI)	2.65 [0.40, 17.52]

Comparison 12. HLPP vs audiometric testing (agriculture students, long‐term, 3‐year and 16‐year follow‐up) ‐ RCT

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 STS Show forest plot	1		Odds Ratio (Fixed, 95% CI)	Subtotals only
Open in figure viewer Analysis 12.1 Comparison 12 HLPP vs audiometric testing (agriculture students, long‐term, 3‐year and 16‐year follow‐up) ‐ RCT, Outcome 1 STS.
1.1 3‐year follow‐up	1		Odds Ratio (Fixed, 95% CI)	0.85 [0.29, 2.44]
1.2 16‐year follow‐up	1		Odds Ratio (Fixed, 95% CI)	0.94 [0.46, 1.91]

Comparison 13. HLPP with daily noise‐exposure monitoring with feedback vs annual audiometry (long‐term) ‐ ITS

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 HL (dB/year at 2, 3 and 4 kHz) Δ level Show forest plot	1		rate of hearing loss (Random, 95% CI)	Totals not selected
Open in figure viewer Analysis 13.1 Comparison 13 HLPP with daily noise‐exposure monitoring with feedback vs annual audiometry (long‐term) ‐ ITS, Outcome 1 HL (dB/year at 2, 3 and 4 kHz) Δ level.
1.1 intervention ‐ controlled for age, gender, baseline hearing	1		rate of hearing loss (Random, 95% CI)	0.0 [0.0, 0.0]
1.2 control ‐ controlled for age, gender, baseline hearing	1		rate of hearing loss (Random, 95% CI)	0.0 [0.0, 0.0]
1.3 intervention minus control ‐ controlled for age, gender, baseline hearing	1		rate of hearing loss (Random, 95% CI)	0.0 [0.0, 0.0]
1.4 intervention ‐ controlled for age, gender, baseline hearing and initial rate of HL	1		rate of hearing loss (Random, 95% CI)	0.0 [0.0, 0.0]
1.5 control ‐ controlled for age, gender, baseline hearing and initial rate of HL	1		rate of hearing loss (Random, 95% CI)	0.0 [0.0, 0.0]
1.6 intervention minus control ‐ controlled for age, gender, baseline hearing and initial rate of HL	1		rate of hearing loss (Random, 95% CI)	0.0 [0.0, 0.0]
2 HL (dB/year at 2, 3 and 4 kHz) slope Show forest plot	1		rate of hearing loss (Fixed, 95% CI)	Totals not selected
Open in figure viewer Analysis 13.2 Comparison 13 HLPP with daily noise‐exposure monitoring with feedback vs annual audiometry (long‐term) ‐ ITS, Outcome 2 HL (dB/year at 2, 3 and 4 kHz) slope.
2.1 intervention ‐ controlled for age, gender, baseline hearing	1		rate of hearing loss (Fixed, 95% CI)	0.0 [0.0, 0.0]
2.2 control ‐ controlled for age, gender, baseline hearing	1		rate of hearing loss (Fixed, 95% CI)	0.0 [0.0, 0.0]
2.3 intervention minus control ‐ controlled for age, gender, baseline hearing	1		rate of hearing loss (Fixed, 95% CI)	0.0 [0.0, 0.0]
2.4 intervention ‐ controlled for age, gender, baseline hearing and initial rate of HL	1		rate of hearing loss (Fixed, 95% CI)	0.0 [0.0, 0.0]
2.5 control ‐ controlled for age, gender, baseline hearing and initial rate of HL	1		rate of hearing loss (Fixed, 95% CI)	0.0 [0.0, 0.0]
2.6 intervention minus control ‐ controlled for age, gender, baseline hearing and initial rate of HL	1		rate of hearing loss (Fixed, 95% CI)	0.0 [0.0, 0.0]

Comparison 14. Follow‐up exam after initial STS vs no exam (long‐term)

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 Hearing loss change (STS) Show forest plot	1	1317	Odds Ratio (M‐H, Fixed, 95% CI)	0.87 [0.56, 1.36]
Open in figure viewer Analysis 14.1 Comparison 14 Follow‐up exam after initial STS vs no exam (long‐term), Outcome 1 Hearing loss change (STS).

Comparison 15. Well‐implemented HLPP vs less well‐implemented (long‐term, 1‐year follow‐up)

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 STS Show forest plot	1	341	Risk Ratio (M‐H, Fixed, 95% CI)	0.36 [0.09, 1.42]
Open in figure viewer Analysis 15.1 Comparison 15 Well‐implemented HLPP vs less well‐implemented (long‐term, 1‐year follow‐up), Outcome 1 STS.

Comparison 16. Well‐implemented HLPP vs less well‐implemented (long‐term > 5‐year follow‐up)

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 Hearing loss change STS/at 4 kHz Show forest plot	3	16301	OR (Random, 95% CI)	0.40 [0.23, 0.69]
Open in figure viewer Analysis 16.1 Comparison 16 Well‐implemented HLPP vs less well‐implemented (long‐term > 5‐year follow‐up), Outcome 1 Hearing loss change STS/at 4 kHz.
1.1 Adera 2000	1	15345	OR (Random, 95% CI)	0.26 [0.14, 0.47]
1.2 Adera 1993	1	692	OR (Random, 95% CI)	0.35 [0.19, 0.65]
1.3 Brink 2000	1	264	OR (Random, 95% CI)	0.62 [0.40, 0.97]

Comparison 17. HLPP 12‐hour shift vs HLPP 8‐hour shift (long‐term 1‐year follow‐up)

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 Hearing loss change over 1 year at 4 kHz Show forest plot	1		Mean Difference (IV, Fixed, 95% CI)	Totals not selected
Open in figure viewer Analysis 17.1 Comparison 17 HLPP 12‐hour shift vs HLPP 8‐hour shift (long‐term 1‐year follow‐up), Outcome 1 Hearing loss change over 1 year at 4 kHz.

Comparison 18. HLPP vs non‐exposed workers (long‐term 1‐year follow‐up)

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 hearing loss STS Show forest plot	1		Risk Ratio (Random, 95% CI)	3.38 [1.23, 9.32]
Open in figure viewer Analysis 18.1 Comparison 18 HLPP vs non‐exposed workers (long‐term 1‐year follow‐up), Outcome 1 hearing loss STS.
1.1 low‐exposed engineers	1		Risk Ratio (Random, 95% CI)	2.07 [0.27, 15.99]
1.2 medium‐exposed infantry	1		Risk Ratio (Random, 95% CI)	2.82 [0.37, 21.57]
1.3 high‐exposed artillery	1		Risk Ratio (Random, 95% CI)	4.69 [1.13, 19.51]

Comparison 19. Improved HLPP vs non‐exposed workers (long‐term 1‐year follow‐up)

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 hearing loss STS Show forest plot	1		Risk Ratio (Fixed, 95% CI)	Totals not selected
Open in figure viewer Analysis 19.1 Comparison 19 Improved HLPP vs non‐exposed workers (long‐term 1‐year follow‐up), Outcome 1 hearing loss STS.
1.1 high‐exposed artillery	1		Risk Ratio (Fixed, 95% CI)	0.0 [0.0, 0.0]

Comparison 20. HLPP vs non‐exposed workers (long‐term > 5‐year follow‐up)

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 Hearing loss change at 4 kHz/STS (5‐year follow‐up) Show forest plot	4	2231	effect size (Fixed, 95% CI)	0.05 [‐0.05, 0.16]
Open in figure viewer Analysis 20.1 Comparison 20 HLPP vs non‐exposed workers (long‐term > 5‐year follow‐up), Outcome 1 Hearing loss change at 4 kHz/STS (5‐year follow‐up).
1.1 Pell hearing loss 10 dB	1	628	effect size (Fixed, 95% CI)	‐0.1 [‐0.27, 0.07]
1.2 Pell hearing loss 15 to 35 dB	1	559	effect size (Fixed, 95% CI)	0.09 [‐0.11, 0.29]
1.3 Pell hearing loss 40 dB	1	385	effect size (Fixed, 95% CI)	0.18 [‐0.06, 0.42]
1.4 Lee‐Feldstein	1	474	effect size (Fixed, 95% CI)	0.29 [‐0.07, 0.66]
1.5 Hager	1	43	effect size (Fixed, 95% CI)	‐0.1 [‐0.72, 0.52]
1.6 Gosztonyi	1	142	effect size (Fixed, 95% CI)	0.15 [‐0.18, 0.48]
2 Hazard of STS Show forest plot	1		Hazard Ratio (Random, 95% CI)	3.78 [2.69, 5.31]
Open in figure viewer Analysis 20.2 Comparison 20 HLPP vs non‐exposed workers (long‐term > 5‐year follow‐up), Outcome 2 Hazard of STS.
2.1 80 to 85 dB‐years	1		Hazard Ratio (Random, 95% CI)	2.10 [1.26, 3.49]
2.2 85 to 90 dB‐years	1		Hazard Ratio (Random, 95% CI)	3.00 [2.27, 3.96]
2.3 90 to 95 dB‐years	1		Hazard Ratio (Random, 95% CI)	3.30 [2.76, 3.94]
2.4 95 to 100 dB‐years	1		Hazard Ratio (Random, 95% CI)	4.60 [3.86, 5.48]
2.5 More than 100 dB‐years	1		Hazard Ratio (Random, 95% CI)	6.60 [5.56, 7.84]

Comparison 21. HLPP vs non‐exposed sensitivity analysis (long‐term, 5‐year follow‐up)

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 Hearing loss change at 4kHz / STS Show forest plot	3		effect size (Fixed, 95% CI)	0.17 [‐0.06, 0.40]
Open in figure viewer Analysis 21.1 Comparison 21 HLPP vs non‐exposed sensitivity analysis (long‐term, 5‐year follow‐up), Outcome 1 Hearing loss change at 4kHz / STS.
1.1 Lee‐Feldstein	1		effect size (Fixed, 95% CI)	0.29 [‐0.07, 0.66]
1.2 Hager	1		effect size (Fixed, 95% CI)	‐0.1 [‐0.72, 0.52]
1.3 Gosztonyi	1		effect size (Fixed, 95% CI)	0.15 [‐0.18, 0.48]

Figure 1

PRISMA Study flow diagram

Figure 2

Risk of bias graph: review authors' judgements about each risk of bias item presented as percentages across all included studies. Please note that the blank space corresponds to the studies that have an ITS study design.

Figure 3

Risk of bias summary: review authors' judgements about each risk of bias item for each included study. Please note that the blank spaces correspond to the studies that have an ITS study design.

Analysis 1.1

Comparison 1 Legislation to decrease noise exposure (long‐term) ‐ ITS, Outcome 1 Immediate change in level.

Analysis 1.2

Comparison 1 Legislation to decrease noise exposure (long‐term) ‐ ITS, Outcome 2 Change in slope.

Analysis 2.1

Comparison 2 HPD (muffs) with instructions vs without instructions (immediate) ‐ RCT, Outcome 1 Noise attenuation at 0.5 kHz (REAT).

Analysis 2.2

Comparison 2 HPD (muffs) with instructions vs without instructions (immediate) ‐ RCT, Outcome 2 Noise attenuation at 1 kHz (REAT).

Analysis 2.3

Comparison 2 HPD (muffs) with instructions vs without instructions (immediate) ‐ RCT, Outcome 3 Noise attenuation at 2 kHz (REAT).

Analysis 2.4

Comparison 2 HPD (muffs) with instructions vs without instructions (immediate) ‐ RCT, Outcome 4 Noise attenuation at 3 kHz (REAT).

Analysis 2.5

Comparison 2 HPD (muffs) with instructions vs without instructions (immediate) ‐ RCT, Outcome 5 Noise attenuation at 4 kHz (REAT).

Analysis 2.6

Comparison 2 HPD (muffs) with instructions vs without instructions (immediate) ‐ RCT, Outcome 6 Noise attenuation at 6 kHz (REAT).

Analysis 2.7

Comparison 2 HPD (muffs) with instructions vs without instructions (immediate) ‐ RCT, Outcome 7 Noise attenuation at 8 kHz (REAT).

Analysis 3.1

Comparison 3 HPD (plugs) with instructions vs without instructions (immediate) ‐ RCT, Outcome 1 Noise attenuation at 0.5 kHz (REAT).

Analysis 3.2

Comparison 3 HPD (plugs) with instructions vs without instructions (immediate) ‐ RCT, Outcome 2 Noise attenuation at 1 kHz (REAT).

Analysis 3.3

Comparison 3 HPD (plugs) with instructions vs without instructions (immediate) ‐ RCT, Outcome 3 Noise attenuation at 2 kHz (REAT).

Analysis 3.4

Comparison 3 HPD (plugs) with instructions vs without instructions (immediate) ‐ RCT, Outcome 4 Noise attenuation at 3 kHz (REAT).

Analysis 3.5

Comparison 3 HPD (plugs) with instructions vs without instructions (immediate) ‐ RCT, Outcome 5 Noise attenuation at 4 kHz (REAT).

Analysis 3.6

Comparison 3 HPD (plugs) with instructions vs without instructions (immediate) ‐ RCT, Outcome 6 Noise attenuation at 6 kHz (REAT).

Analysis 3.7

Comparison 3 HPD (plugs) with instructions vs without instructions (immediate) ‐ RCT, Outcome 7 Noise attenuation at 8 kHz (REAT).

Analysis 3.8

Comparison 3 HPD (plugs) with instructions vs without instructions (immediate) ‐ RCT, Outcome 8 Mean noise attenuation over 0.5, 1, 2, 3, 4, 6, 8 kHz (REAT).

Analysis 4.1

Comparison 4 HPD (plugs) lower noise reduction rate (NRR) with instructions vs higher NRR without instructions (immediate) ‐ RCT, Outcome 1 Mean attenuation at 0.5, 1, 2, 3, 4, 6, 8 kHz.

Analysis 5.1

Comparison 5 HPD with ANC vs without ANC (immediate), Outcome 1 Noise attenuation (dB).

Analysis 5.2

Comparison 5 HPD with ANC vs without ANC (immediate), Outcome 2 TTS at 1 kHz (before exposure ‐ after exposure ).

Analysis 5.3

Comparison 5 HPD with ANC vs without ANC (immediate), Outcome 3 TTS at 2 kHz (before exposure ‐ after exposure ).

Analysis 5.4

Comparison 5 HPD with ANC vs without ANC (immediate), Outcome 4 TTS at 4 kHz (before exposure ‐ after exposure ).

Analysis 5.5

Comparison 5 HPD with ANC vs without ANC (immediate), Outcome 5 TTS at 6 kHz (before exposure ‐ after exposure ).

Analysis 5.6

Comparison 5 HPD with ANC vs without ANC (immediate), Outcome 6 TTS at 8 kHz (before exposure ‐ after exposure ).

Analysis 6.1

Comparison 6 Custom‐moulded musician HPD (plugs) with higher versus HPD (plugs) with lower noise attenuation, Outcome 1 Noise attenuation dB(A).

Analysis 7.1

Comparison 7 HPD (various) noise attenuation (immediate), Outcome 1 Noise attenuation (dB).

Analysis 8.1

Comparison 8 HLPP with noise level indicator vs no noise level indicator, Outcome 1 Change in noise levels at 2 months' follow‐up.

Analysis 8.2

Comparison 8 HLPP with noise level indicator vs no noise level indicator, Outcome 2 Change in noise levels at 4 months' follow‐up.

Analysis 9.1

Comparison 9 HLPP with extensive information vs information only, Outcome 1 Change in noise levels at 2 months' follow‐up.

Analysis 9.2

Comparison 9 HLPP with extensive information vs information only, Outcome 2 Change in noise levels at 4 months' follow‐up.

Analysis 10.1

Comparison 10 V‐51‐R plug versus EAR plug (immediate), Outcome 1 TTS at 0.5 kHz (Hearing loss before exposure ‐ after exposure ).

Analysis 10.2

Comparison 10 V‐51‐R plug versus EAR plug (immediate), Outcome 2 TTS at 1 kHz (before exposure ‐ after exposure ).

Analysis 10.3

Comparison 10 V‐51‐R plug versus EAR plug (immediate), Outcome 3 TTS at 2 kHz (before exposure ‐ after exposure ).

Analysis 10.4

Comparison 10 V‐51‐R plug versus EAR plug (immediate), Outcome 4 TTS at 3 kHz (before exposure ‐ after exposure ).

Analysis 10.5

Comparison 10 V‐51‐R plug versus EAR plug (immediate), Outcome 5 TTS at 4 kHz (before exposure ‐ after exposure).

Analysis 10.6

Comparison 10 V‐51‐R plug versus EAR plug (immediate), Outcome 6 TTS at 6 kHz (before exposure ‐ after exposure).

Analysis 11.1

Comparison 11 Earmuffs vs earplugs (long‐term), Outcome 1 Hearing loss change over 3 years (4 kHz / STS).

Analysis 12.1

Comparison 12 HLPP vs audiometric testing (agriculture students, long‐term, 3‐year and 16‐year follow‐up) ‐ RCT, Outcome 1 STS.

Analysis 13.1

Comparison 13 HLPP with daily noise‐exposure monitoring with feedback vs annual audiometry (long‐term) ‐ ITS, Outcome 1 HL (dB/year at 2, 3 and 4 kHz) Δ level.

Analysis 13.2

Comparison 13 HLPP with daily noise‐exposure monitoring with feedback vs annual audiometry (long‐term) ‐ ITS, Outcome 2 HL (dB/year at 2, 3 and 4 kHz) slope.

Analysis 14.1

Comparison 14 Follow‐up exam after initial STS vs no exam (long‐term), Outcome 1 Hearing loss change (STS).

Analysis 15.1

Comparison 15 Well‐implemented HLPP vs less well‐implemented (long‐term, 1‐year follow‐up), Outcome 1 STS.

Analysis 16.1

Comparison 16 Well‐implemented HLPP vs less well‐implemented (long‐term > 5‐year follow‐up), Outcome 1 Hearing loss change STS/at 4 kHz.

Analysis 17.1

Comparison 17 HLPP 12‐hour shift vs HLPP 8‐hour shift (long‐term 1‐year follow‐up), Outcome 1 Hearing loss change over 1 year at 4 kHz.

Analysis 18.1

Comparison 18 HLPP vs non‐exposed workers (long‐term 1‐year follow‐up), Outcome 1 hearing loss STS.

Analysis 19.1

Comparison 19 Improved HLPP vs non‐exposed workers (long‐term 1‐year follow‐up), Outcome 1 hearing loss STS.

Analysis 20.1

Comparison 20 HLPP vs non‐exposed workers (long‐term > 5‐year follow‐up), Outcome 1 Hearing loss change at 4 kHz/STS (5‐year follow‐up).

Analysis 20.2

Comparison 20 HLPP vs non‐exposed workers (long‐term > 5‐year follow‐up), Outcome 2 Hazard of STS.

Analysis 21.1

Comparison 21 HLPP vs non‐exposed sensitivity analysis (long‐term, 5‐year follow‐up), Outcome 1 Hearing loss change at 4kHz / STS.

Summary of findings for the main comparison. Stricter legislation for noise exposure

Stricter legislation compared with existing legislation for noise exposure
Patient or population: workers with noise exposure Settings: coal mines Intervention: stricter legislation Comparison: existing legislation
Outcomes	*Illustrative comparative risks (95% CI)**		No of observations (studies)	Quality of the evidence (GRADE)	Comments
	Assumed risk	Corresponding risk
	Existing legislation	Stricter legislation
Immediate change in level in year 2000 (noise level at work as PEL dose in dB(A); range 0 to 6400, log scale) 1 year	The mean noise levels during pre‐intervention years were 56.9 PEL dose	The mean noise exposure level after introduction was 27.70 PEL dose lower (36.1 lower to 19.3 lower PEL dose)	14 years pre‐intervention and 4 years post‐intervention (1 ITS)	⊕⊝⊝⊝ very low¹	The reduction of 27.7 PEL dose translates to about 4.5 dB(A)
Change in slope after introduction (noise level at work as PEL dose in dB(A); range 0 to 6400, log scale) 4 years	The mean noise levels during pre‐intervention years were 56.9 PEL dose	The mean change in level of noise exposure per year after introduction was 2.10 PEL dose lower (4.90 lower to 0.70 PEL dose higher)	14 years pre‐intervention and 4 years post‐intervention (1 ITS)	⊕⊝⊝⊝ very low¹
The basis for the assumed risk* (e.g. the median control group risk across studies) is provided in footnotes. The corresponding risk (and its 95% confidence interval) is based on the assumed risk in the comparison group and the absolute effect of the intervention (and its 95% CI). CI: Confidence interval; PEL: permissible exposure level
GRADE Working Group grades of evidence High quality: we are very confident that the true effect lies close to that of the estimate of the effect Moderate quality: we are moderately confident in the effect estimate; the true effect is likely to be close to the estimate of effect, but there is a possibility that it is substantially different Low quality: our confidence in the effect estimate is limited; the true effect may be substantially different from the estimate of the effect Very low quality: we have very little confidence in the effect estimate; the true effect is likely to be substantially different from the estimate of effect
¹We downgraded by one level from low to very low because there is only one study and it has a high risk of bias.

Summary of findings for the main comparison. Stricter legislation for noise exposure

Summary of findings 2. Earplugs with instruction versus without instruction (noise exposure)

Earplugs with instruction compared with no instruction for noise reduction
Patient or population: workers with exposure to noise Settings: industrial Intervention: instruction on how to insert earplugs Comparison: no instruction
Outcomes	*Illustrative comparative risks (95% CI)**		No of participants (studies)	Quality of the evidence (GRADE)	Comments
	Assumed risk	Corresponding risk
	Without instruction	With instruction
Mean noise attenuation over 0.5, 1, 2, 3, 4, 6, 8 kHz (dB) Immediate follow‐up	The mean noise attenuation ranged across frequencies from 5.5 to 25.9 dB	The mean noise attenuation in the intervention groups was 8.59 dB higher (6.92 dB higher to 10.25 dB higher)	140 participants (2 RCTs)	⊕⊕⊕⊝ moderate¹
The basis for the assumed risk* (e.g. the median control group risk across studies) is provided in footnotes. The corresponding risk (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). CI: Confidence interval
GRADE Working Group grades of evidence High quality: we are very confident that the true effect lies close to that of the estimate of the effect Moderate quality: we are moderately confident in the effect estimate; the true effect is likely to be close to the estimate of effect, but there is a possibility that it is substantially different Low quality: our confidence in the effect estimate is limited; the true effect may be substantially different from the estimate of the effect Very low quality: we have very little confidence in the effect estimate; the true effect is likely to be substantially different from the estimate of effect
¹We downgraded from high quality by one level because of imprecision due to small number of participants.

Summary of findings 2. Earplugs with instruction versus without instruction (noise exposure)

Summary of findings 3. Training plus exposure information compared to training (noise exposure)

Exposure information compared with training as usual for noise exposure
Patient or population: workers exposed to noise Settings: construction industry Intervention: provision of noise level indicator Comparison: safety training as usual
Outcomes	*Illustrative comparative risks (95% CI)**		No of participants (studies)	Quality of the evidence (GRADE)	Comments
	Assumed risk	Corresponding risk
	Training as usual	Plus noise level indicator
Change in noise levels at 4 months' follow‐up (dB(A))	The mean noise level in the control group ranged from 87.1 to 89 dB(A)	The mean noise level in the intervention groups was 0.3 dB(A) higher (2.31 dB(A) lower to 2.91 dB(A) higher	176 (1 study, RCT)	⊕⊕⊝⊝ low¹
The basis for the assumed risk* (e.g. the median control group risk across studies) is provided in footnotes. The corresponding risk (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). CI: Confidence interval
GRADE Working Group grades of evidence High quality: we are very confident that the true effect lies close to that of the estimate of the effect Moderate quality: we are moderately confident in the effect estimate; the true effect is likely to be close to the estimate of effect, but there is a possibility that it is substantially different Low quality: our confidence in the effect estimate is limited; the true effect may be substantially different from the estimate of the effect Very low quality: we have very little confidence in the effect estimate; the true effect is likely to be substantially different from the estimate of effect
¹We downgraded by two levels from high to low because of high risk of bias and imprecision.

Summary of findings 3. Training plus exposure information compared to training (noise exposure)

Summary of findings 4. Earmuffs versus earplugs (hearing loss)

Earmuffs compared with earplugs for noise‐induced hearing loss
Patient or population: workers exposed to 88‐94 dB(A) Settings: shipyard Intervention: most wearing earmuffs Comparison: most wearing earplugs
Outcomes	*Illustrative comparative risks (95% CI)**		Relative effect (95% CI)	No of participants (studies)	Quality of the evidence (GRADE)	Comments
	Assumed risk	Corresponding risk
	Earplugs	Earmuffs
Hearing loss change over 3 years (4 kHz/STS) 2 to 3 years' follow‐up	High risk population		OR 0.8 (0.63 to 1.03 )	3242 (2 CBA studies)	⊕⊝⊝⊝ very low¹	At lower exposures the results were too heterogeneous to be combined
	42 per 1000	34 per 1000 (26 to 43)
The basis for the assumed risk* (e.g. the median control group risk across studies) is provided in footnotes. The corresponding risk (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). CI: Confidence interval; OR: Odds Ratio; STS: standard threshold shift
GRADE Working Group grades of evidence High quality: we are very confident that the true effect lies close to that of the estimate of the effect Moderate quality: we are moderately confident in the effect estimate; the true effect is likely to be close to the estimate of effect, but there is a possibility that it is substantially different Low quality: our confidence in the effect estimate is limited; the true effect may be substantially different from the estimate of the effect Very low quality: we have very little confidence in the effect estimate; the true effect is likely to be substantially different from the estimate of effect
¹We downgraded from low quality to very low quality because of high risk of bias in both studies.

Summary of findings 4. Earmuffs versus earplugs (hearing loss)

Summary of findings 5. Hearing loss prevention programme compared to audiometric testing (hearing loss)

Hearing loss prevention programme (HLPP) compared to audiometric testing
Patient or population: agricultural students without hearing loss Settings: agricultural schools Intervention: HLPP with information Comparison: audiometric testing only
Outcomes	*Illustrative comparative risks (95% CI)**		Relative effect (95% CI)	No of participants (studies)	Quality of the evidence (GRADE)	Comments
	Assumed risk	Corresponding risk
	Audiometric testing only	HLPP with information
Hearing loss STS ≥ 10 dB loss average over 2, 3, 4 kHz in either ear Follow‐up: mean three years	21 per 1000	18 per 1000 (6 to 49)	OR 0.85 (0.29 to 2.44)	687 (1 study, RCT)	⊕⊕⊕⊝ moderate¹
Hearing loss STS ≥ 10 dB hearing loss average over 2, 3, 4 kHz in either ear Follow‐up: mean 16 years	149 per 1000	141 per 1000 (74 to 250)	OR 0.94 (0.46 to 1.91)	355 (1 study, RCT)	⊕⊕⊕⊝ moderate¹
The basis for the assumed risk* (e.g. the median control group risk across studies) is provided in footnotes. The corresponding risk (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). CI: Confidence interval; HLPP; hearing loss prevention programme; OR: Odds ratio; STS: standard threshold shift
GRADE Working Group grades of evidence High quality: we are very confident that the true effect lies close to that of the estimate of the effect Moderate quality: we are moderately confident in the effect estimate; the true effect is likely to be close to the estimate of effect, but there is a possibility that it is substantially different Low quality: our confidence in the effect estimate is limited; the true effect may be substantially different from the estimate of the effect Very low quality: we have very little confidence in the effect estimate; the true effect is likely to be substantially different from the estimate of effect
¹We downgraded one level from high to moderate due to lack of information on randomisation and allocation concealment.

Summary of findings 5. Hearing loss prevention programme compared to audiometric testing (hearing loss)

Summary of findings 6. Hearing loss prevention programme (HLPP) with exposure information compared to HLPP without exposure information (hearing loss)

HLPP with exposure information compared with HLPP without exposure information for noise‐induced hearing loss
Patient or population: workers exposed to noise Settings: aluminium smelter Intervention: exposure information as part of HLPP Comparison: no such information
Outcomes	*Illustrative comparative risks (95% CI)**		No of participants (studies)	Quality of the evidence (GRADE)	Comments
	Assumed risk	Corresponding risk
	Without exposure info	With exposure info
Annual increase in hearing threshold (dB/year at 2,3 and 4 kHz) 4‐year follow‐up	The mean hearing loss rate in the control group was 1.0 dB per year	The mean hearing loss rate in the intervention groups was 0.82 dB/year lower (1.86 lower to 0.22 higher)	312 (1 CBA study)	⊕⊝⊝⊝ very low¹	Matched for age, gender, baseline hearing loss and baseline hearing
The basis for the assumed risk* (e.g. the median control group risk across studies) is provided in footnotes. The corresponding risk (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). CI: Confidence interval; HLPP: hearing loss prevention programme
GRADE Working Group grades of evidence High quality: we are very confident that the true effect lies close to that of the estimate of the effect Moderate quality: we are moderately confident in the effect estimate; the true effect is likely to be close to the estimate of effect, but there is a possibility that it is substantially different Low quality: our confidence in the effect estimate is limited; the true effect may be substantially different from the estimate of the effect Very low quality: we have very little confidence in the effect estimate; the true effect is likely to be substantially different from the estimate of effect
¹We downgraded by one level from low to very low because of high risk of bias.

Summary of findings 6. Hearing loss prevention programme (HLPP) with exposure information compared to HLPP without exposure information (hearing loss)

Summary of findings 7. Well‐implemented hearing loss prevention programme (HLPP) compared to less well‐implemented HLPP (hearing loss)

Well‐implemented hearing loss prevention programme (HLPP) compared to less well‐implemented HLPP for hearing loss
Patient or population: workers Settings: exposure to noise Intervention: well‐implemented HLPP Comparison: less well‐implemented HLPP
Outcomes	*Illustrative comparative risks (95% CI)**		Relative effect (95% CI)	No of participants (studies)	Quality of the evidence (GRADE)	Comments
	Assumed risk	Corresponding risk
	Less well‐implemented HLPP	Well‐implemented HLPP
Hearing loss STS > 10 dB change average over 2, 3 and 4 kHz¹ Follow‐up: mean 9.3 years	86 per 1000	36 per 1000 (21 to 61)²	OR 0.40 (0.23 to 0.69)³	16,301 (3 studies⁴)	⊕⊝⊝⊝ very low⁵	SMD 0.26 (0.14 to 0.47)
The basis for the assumed risk* (e.g. the median control group risk across studies) is provided in footnotes. The corresponding risk (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). CI: Confidence interval; HLPP: hearing loss prevention programme; OR: Odds ratio; STS: standard threshold shift
GRADE Working Group grades of evidence High quality: we are very confident that the true effect lies close to that of the estimate of the effect Moderate quality: we are moderately confident in the effect estimate; the true effect is likely to be close to the estimate of effect, but there is a possibility that it is substantially different Low quality: our confidence in the effect estimate is limited; the true effect may be substantially different from the estimate of the effect Very low quality: we have very little confidence in the effect estimate; the true effect is likely to be substantially different from the estimate of effect
¹STS used in two studies, change of mean 4 kHz threshold in one study. ²Number of events based on median event rate in included studies. ³Result from the meta‐analysis of three studies. ⁴One extra study provided similar evidence but could not be combined in the meta‐analysis. ⁵We downgraded by one level from low to very low because of risk of bias due to lack of adjustment for age and hearing loss.

Summary of findings 7. Well‐implemented hearing loss prevention programme (HLPP) compared to less well‐implemented HLPP (hearing loss)

Summary of findings 8. Hearing loss prevention programme (HLPP) compared to non‐exposed workers (hearing loss)

Hearing loss prevention programme (HLPP) compared to non‐exposed workers
Patient or population: workers Settings: exposure to noise Intervention: HLPP Comparison: non‐exposed workers
Outcomes	*Illustrative comparative risks (95% CI)**		Relative effect (95% CI)	No of participants (studies)	Quality of the evidence (GRADE)	Comments
	Assumed risk	Corresponding risk
	Non‐exposed workers	HLPP
Hearing loss Change in hearing threshold at 4 kHz in dB Follow‐up: mean five years	The mean hearing loss in the control groups was 3.6 dB at 4 kHz¹	The mean hearing loss in the intervention groups was 1.8 dB higher (0.6 lower to 4.2 higher)		1846 (3 studies²)	⊕⊝⊝⊝ very low^3,4	pooled effect size 0.17 (95% CI ‐0.06 to 0.40) recalculated into dBs
The basis for the assumed risk* (e.g. the median control group risk across studies) is provided in footnotes. The corresponding risk (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). CI: Confidence interval; HLPP: hearing loss prevention programme; SMD: standardised mean difference
GRADE Working Group grades of evidence High quality: we are very confident that the true effect lies close to that of the estimate of the effect Moderate quality: we are moderately confident in the effect estimate; the true effect is likely to be close to the estimate of effect, but there is a possibility that it is substantially different Low quality: our confidence in the effect estimate is limited; the true effect may be substantially different from the estimate of the effect Very low quality: we have very little confidence in the effect estimate; the true effect is likely to be substantially different from the estimate of effect
¹Assumed increase of hearing threshold: median of three studies with respectively 3.4, 3.6 and 5.2 dB increase in hearing threshold at 4 kHz after five years' follow‐up. ²Results from three of five studies included in sensitivity analysis because one study was at serious risk of bias and one other study showed that in spite of hearing protection workers were still more at risk than non‐exposed workers. ³We downgraded by one level from low to very low because three studies did not adjust for age and hearing loss at baseline. ⁴We would have downgraded by one more level because the confidence interval does not exclude a risk of hearing loss similar to exposure to 85 dB(A) but we had already reached a rating of very low quality evidence.

Summary of findings 8. Hearing loss prevention programme (HLPP) compared to non‐exposed workers (hearing loss)

Table 1. Recalculation of study data for review results and meta‐analysis

Küpper 2013 (Outcome: Leq 8 h (dB)^a) ‐ noise exposure of rescue helicopter personnel ‐ case study
Study data						Recalculation ‐ group mean, SD
Helicopter type	Helicopter name	mean	SD	dB min	dB max	variance		mean	SD
with advanced technology	EC 135^b	85.80	4.00	73.00	97.00	16.00		87.9	4.16
	BK 117^b	87.20	4.60	74.00	101.00	21.16
	Bell 206 B Jetranger^c	88.80	4.00	76.00	100.00	16.00
	Bell 206 Longranger II^c	89.80	4.00	77.00	101.00	16.00
without advanced technology	UH 1D^b	86.80	4.00	74.00	98.00	16.00		98.41	4.49
	BO 105^c	91.80	4.00	79.00	103.00	16.00
	Sea King^c	92.60	7.50	78.00	114.00	56.25
	Ecureuil AS350B^b	92.80	4.00	80.00	104.00	16.00
	Alouette IIIb^b	98.40	4.80	85.00	113.00	23.04
	Sikorsky H‐23/UH12^c	99.70	3.90	87.00	111.00	15.21
	Alouette II^b	100.10	4.40	87.00	113.00	19.36
	Sikorsky H‐34^c	101.8	4.00	89.00	113.00	16.00
	Mi‐4^c	109.10	3.50	97.00	117.00	12.25
	Sikorsky H‐37 Mojave^c	111	3.40	99.00	119.00	11.56
Muhr 2016 (Outcome: STS) ‐ hearing loss Swedish military ‐ CBA
Study data				Recalculation
group	follow up mean (month)	# Events	N	follow up (month/year)		per 100 person‐years
						event rate		lnRR	SE
HLPP	8	9	395	0.67		3.4		0.002	0.379
non‐exposed	13	31	839	1.08		3.4
Muhr 2006 (Outcome: STS) ‐ hearing loss Swedish military ‐ CBA
Study data				Recalculation
group	follow up mean (month)	# Events	N	group	follow up (year)	# Events	N	per 100 person‐years
								event rate	lnRR	SE
HLPP (low‐exposed)	9.25	11	291	HLPP (low‐exposed)	0.77	11	291	4.9	0.73	1.04
HLPP (medium‐exposed)		13	252	non‐exposed (split 1)	0.92	1	46	2.37
HLPP (high‐exposed)		35	204	HLPP (medium‐exposed)	0.77	13	252	6.69	1.04	1.04
non‐exposed	11	4	138	non‐exposed (split 2)	0.92	1	46	2.37
				HLPP (high‐exposed)	0.77	35	204	22.26	1.55	0.73
				non‐exposed (split 3)	0.92	2	46	4.74
				non‐exposed (all)	0.92	4	138	3.16
				low‐exposed vs non‐exposed (all)					0.439	0.584
				medium‐exposed vs non‐exposed (all)					0.750	0.572
				high‐exposed vs non‐exposed (all)					1.951	0.528
^aBased on task analysis and helicopter noise data, task analysis is based on measurements of type and duration of tasks per rescue operation of four bases over 1 year (total, 2726 rescue operations). ^bStudy authors obtained helicopter noise data from own measurements (n = 3 per helicopter). ^cStudy authors obtained helicopter noise data from other studies.

Table 1. Recalculation of study data for review results and meta‐analysis

Table 2. Assessment of quality of evidence (GRADE)

Comparison	N Studies	1. RoB?	2. Inconsistent?	3. Indirect?	4. Imprecise?	5. Pub bias?	6. Large ES?	7. DR?	8. Opp Conf	Quality^a
Outcome noise
Legislation vs no legislation	1 ITS	yes	1 study	no	no	1 study	yes	no	no	very low (1)
One HPD vs another HPD	1 RCT 4 CBA	2 yes	no	no	no	not shown	no	no	no	low (1)
HPD+Instruction vs HPD‐instruction	2 RCT	2 no	no	no	yes	not shown	na	na	na	moderate (4)
Information vs no information	1 RCT (2 arms)	1 yes	1 study	no	yes	1 study	na	na	na	low (1, 4)
Outcome hearing loss
One HPD vs another HPD (TTS)	2 CBA									no data
Muffs vs plugs	2 CBA	2 yes	no	no	yes	not shown	no	no	no	very low (1,4)
Frequent HPD vs less frequent use	1 CBA	1 yes	1 study	no	yes	1 study	no	no	no	very low (1)
HLPP vs audiometry	1 RCT	1 yes	1 study	no	no	1 study	na	na	na	moderate (1)
HLPP+exposure information vs HLPP‐information	1 CBA	1 yes	1 study	no	yes	1 study	no	no	no	very low (1,4)
Frequent HPD in HLPP vs less	5 CBA	5 yes	no	no	yes	not shown	no	no	no	very low (1,4)
HLPP vs no exposure	7 CBA	7 yes	no	no	yes	not shown	no	no	no	very low (1,4)
Follow‐up vs no follow‐up	1 CBA	1 yes	1 study	no	yes	1 study	no	no	no	very low (1,4)
HLPP+long shifts vs HLPP normal	1 CBA	1 yes	1 study	no	yes	1 study	no	no	no	very low (1,4)
1‐5 Reasons for downgrading: 1. Risk of bias/Limitations in study design 2. Inconsistency between studies. 3. Indirectness of PICO 4. Imprecision of the results 5. Publication bias. 6‐8 Reasons for upgrading: 6. Large effect size. 7. Dose‐repsonse relationship 8. Confounding opposes the direction of the effect; na= not applicable; 1 study = only one study available and impossible to assess consistency or publication bias ^aFinal grading of quality of evidence, between brackets domain that led to down/upgrading the quality.

Table 2. Assessment of quality of evidence (GRADE)

Table 3. Contents of hearing loss prevention programmes

Study	Described as HLPP	HPD provided	Noise measurements	Technical measures	Administrative measures	Audiometry
Adera 1993	?	Enforced mandatory wearing of hearing protection	Personal dosimeter twice a year	?	?	Audiometric booth ANSI‐OSHA
Adera 2000	HLPP	? based on Aldera 1993 we assumed that excellent implementation meant better use of hearing protection	?	?	?	Audiogram taken
Berg 2009	HCP	Beside educational intervention, hearing protection devices were provided free to students and replaced regularly	Students were given opportunity to use sound level meter unaffiliated	Not part of the programme	Not part of the programme	Yearly audiometric testing, calibrated per ANSI standard with Hughson‐Westlake modification of the ascending threshold technique
Brink 2002	HCP	?	Area‐wide sound level surveys	?	?	Annual audiometric evaluation calibrated Bekesy audiometer ANSI
Davies 2008	HCP	Hearing protection was one element	Noise monitoring was one element	Engineering controls were one element	Administrative controls were one element	Audiometric evaluation by certified audiometric technicians
Erlandsson 1980	?	?	Personal noise dosimeters	?	?	Calibrated ISO r389
Gosztonyi 1975	HCP	Earmuffs mandatory in noise areas	Calibrated personal dosimeters sound level meter in all shop areas	?	?	Soundproof booth ANSI s3.1‐1960
Hager 1982	Walsh‐Healy standard; OSHA	Yes, mandatory use of approved protection	?	Gradual continuous engineering control wherever, whenever economically feasible	?	Audiometric surveys
Heyer 2011	HCP	? Percent use of hearing protection used as a quality indicator	Used as a quality indicator of the programmes: high quality if any monitoring and worker input reported by focus group	Stated as part of the programme but not possible to evaluate with the study data	Training and education stated as part of the programme but not possible to evaluate with study data	Audiometric testing, quality varies, evaluated as days between two tests, audiometry method not reported
Lee‐Feldstein 1993	?	?	Annual sound surveys	?	?	Automatic audiometer according to ANSI s3.6‐1996
Meyer 1993	HCP	Must be provided with effective HP devices	Identify hazardous noise	?	Detailed follow‐up 3 and 6 months after a STS	?
Muhr 2006	HCP	Earmuffs and or earplugs with level‐dependent function limited to 82 dB(A) with SNR 27 dB	Standardised noise measurements	Risk areas around weapon use	?	Screening audiometry
Muhr 2016	HCP, stated to be stricter than to the one evaluated in Muhr 2006	Mandatory use of HPDs, earmuffs and or earplugs with or without level‐dependent function (enable speech communication), (stated to be stricter recommendations and better devices)	?	safety distances (stated to be stricter)	Mandatory training in HPD use and education in NIHL and noise induced tinnitus, stricter audiometry inclusion criteria for acceptance to military service (≤ 25 dB average HL for the frequencies 0.5 to 8 kHz in both ears, 30 dB HL at one or more frequencies, and 35–40 dB HL at one single frequency) (to exclude mild hearing loss cases presumed to be more vulnerable to HL)	Screening audiometry at begin and end of military service
Nilsson 1980	Routine HCP	?	Individual noise dosimetry over long periods	?	?	Calibrated ISO 389 isolated booth
Pell 1973	?	Mandatory hearing protection	Routine noise level surveys	Noise abatement	?	Automatic Bekesy‐type ANSI calibrated
Reynolds 1990a	HCP	3 specific types of earplugs	Sound survey, noise dosimeters	?	?	Audiometric database
Simpson 1994	Demonstrate excellent HCP practices	?	?	?	?	?
ANSI = American National Standards Institute HCP = hearing conservation programme HL = hearing loss HLPP = hearing loss prevention programme HPD = hearing protection device ISO = International Organization for Standardization OSHA =Occupational Safety and Health Administration SNR = Single Number Rating ? = not reported

Table 3. Contents of hearing loss prevention programmes

Table 4. List of included case studies

Reference ID	Case studies included in review
Reference ID	Number of cases	Type of industry	Country	Intervention^a	Measure^b	Additional information (number of cases)
Azman 2012	1	mining (1)	USA	retro‐fit	noise level, noise dose	description of noise measurement (1), follow‐up (1)
Caillet 2012	1	offshore helicopter (1)	France	all retro‐fit	noise level	description of noise measurement (1), funding (1), conflict of interest (1)
Cockrell 2015	2	manufacturing (2)	USA	all retro‐fit	noise level, dose	description of noise measurement (2)
Golmohammadi 2014	3	steel industry (3)	Iran	all retro‐fit	noise level, dose	description of noise measurement (3), funding (3), conflict of interest (3)
HSE 2013a	57	manufacturing (57)	not reported	new 6 retro‐fit 51	noise level	‐
HSE 2015	2	manufacturing (2)	not reported	all retro‐fit	noise level	‐
Küpper 2013	1	alpine rescue operation (helicopter) (1)	Austria, Switzerland	new	noise level	description of noise measurement, follow‐up, statistical tests used
Maling 2016	8	textile (1), paper shredding (1), manufacturing (6)	USA	new 4, retro‐fit 2, both 2	noise level	‐
Morata 2015	18	manufacturing (15), drilling industry (2), mining (1)	not reported	new 5, retro‐fit 11, both 2	noise level, dose	description of noise measurement (3)
Pan 2016	3	mining (3)	Australia	all retro‐fit	dose	description of noise measurement (2), funding (3), follow‐up (immediate) (3)
Thompson 2015	5	mining(5)	USA	all retro‐fit	noise level, dose	description of noise measurement (1), adverse effects: engine over‐heating (1), time of intervention: 2014/2015 (1)
Wilson 2016	6	manufacturing (6)	not reported	all retro‐fit	noise level	‐
Total	107	manufacturing (88), mining (10), steel (3), drilling (2), helicopter (2), textile (1), paper shredding (1)	Australia (3), Iran (3), France (1), USA (16), Austria and Switzerland (1), nr (26)	retro‐fit (86), new (16), both (4)	noise level, dose	description of noise measurement (14), funding (7), follow‐up (5), conflict of interest (4), adverse effects (1), time of intervention (1), statistical tests used (1)
^aTypes of intervention: installation of completely new equipment (new), intervention to improve existing equipment (e.g. new parts, additional damping material layers) (retro‐fit), or a combination of new and retro‐fit interventions (both). ^bNoise level (including time‐weighted averages or sound pressure levels), dose (including calculations according to OSHA, NIOSH, or MSHA PEL specifications).

Table 4. List of included case studies

Table 5. Results case studies ‐ new equipment

New equipment
Noise source	Intervention	follow‐up	Initial noise level	Noise level after	8 h TWA before	8 h TWA after	Reference ID
Helicopter	Modern helicopter with advanced technology (compared to older helicopters without advanced technology)	short term (1 year)			mean 98.41 (SD 4.49) (n = 10)	mean 87.9 (SD 4.16) (n = 4)	Küpper 2013
Pumps	New high‐pressure coolant pumps have been installed at various metal cutting operations. These new pumps produce more pressure and more volume directly at the cutting tools.	not reported	110 dB	87 dB			Maling 2016
Drill	New injector drill with a sound enclosure for a deep drilling operation	not reported	110 dB	95 dB
Roof fans	Old roof fans were replaced with new high‐efficiency fans	not reported		lowered the noise below the fan
Air gun	Air gun substitution	not reported	94 dB	85 dB			Morata 2015
Fork lifts	Use of tugs instead of fork lifts	not reported	92 dB	72 dB
Alarm system	Change from audible alarm to visual warning and pressure sensor	not reported	95 dB	0 dB
Air wand	Replacement of 45 air wands	not reported	112.8 dB	90.1 dB
Bottling line ‐ rinser‐filler‐capper machine	Purchase of a new bottling line	not reported	89 dB	below 80 dB			HSE 2013
Bottle‐blowers	New bottle‐blowers and segregation	not reported	86‐87 dB	below 83 dB
Glass bottles on transport conveyer	Purchasing new design of bottle transport conveyor	not reported	101 dB	83 dB
Packing machinery ‐ Compressors and compressed‐air exhausts	Purchasing policy and fitted silencers	not reported	above 90 dB	below 85 dB
Bakery machinery	Not purchasing equipment that produced noise level above 85 dB, company’s health and safety adviser would visit the makers of new machinery during its manufacture and conduct a noise assessment to make sure the machinery did not exceed 85 dB	not reported	94 dB	85 dB
Bottle‐laner ‐ bottles banging together on laner conveyor	New machine with guide‐rails	not reported	93‐96 dB	87 dB
	Number of cases: 14		mean before		mean after		mean reduction
	Noise level dB		97.4 dB		77.7 dB		19.7
	TWA dB		98.41 (SD 4.49)		87.9 (SD 4.16)		10.51 (95% CI 15.45 to 5.57)
TWA = time weighted average

Table 5. Results case studies ‐ new equipment

Table 6. Results case studies ‐ acoustic panels and curtains

Acoustic panels and curtains
Noise source	Intervention	Follow‐up	Initial noise level	Noise level after	Dose before	Dose after	Reference ID
Production noise	Door	not reported	85 dB	79 dB			Morata 2015
Blast furnace	Control rooms were redesigned in order to improve acoustical condition: installation of a UPVC window with vacuumed double‐layered glass 80 x 80 cm and double wall for entrance by 90° rotate plus a 2.0 × 1.2 m steel door without glass	not reported	80 dB	52.6 dB			Golmohammadi 2014
Blast furnace	In rest room wall facing to the furnace was made from the armed concrete with a thickness of 20 cm, length of 9 m, and height of 3 m and was located in the entrance by 90° rotate	not reported	86.1 dB	58.4 dB
Blast furnace	Control room and rest room redesigned to improve acoustical condition	not reported			236% (unspecified)	130% (unspecified)
Product impact on multi‐head weigher	Fitted flexible PVC curtains	not reported	92 dB	88 dB			HSE 2013
Packaging lines	Fitted acoustic baffles to ceiling	not reported	Above 90 dB	below 90 dB
Noise from hearing protection zones affecting quieter areas	Erected acoustic panels and automatic doors between hearing protection zones and quieter areas	not reported	Above 90 dB	below 85 dB
Filler pump	Improved efficiency of pump and added acoustic hood	not reported	96 dB	86 dB
Compressed air in bottle transportation	Acoustic side panels fitted	not reported	85–86 dB	73 dB
Product impact on hoppers	Flexible PVC curtains fitted	not reported	Above 90 dB	83 dB
	Number of cases: 10		mean before	mean after	mean reduction
	noise level dB		88.3	77.2	11.1
	Dose % (unspecified)		236	130	106

Table 6. Results case studies ‐ acoustic panels and curtains

Table 7. Results case studies ‐ damping material and silencers

Damping material and silencers
Noise source	Intervention	Follow‐up	Initialnoise level	Noise level after	8 h TWA before	8 h TWA after	Dose before	Dose after	Reference ID
Confetti machine	Damped machine surfaces: Replaced vacuums with small cyclones that were quieter and had fewer clogs, Installed conveyors to carry the paper into the disintegrators	not reported	95 dB	85 dB					Maling 2016
Production noise	Installation of sound absorbing panels, shields, covers, insulation, sheeting, installation of mufflers for fans and solenoids, reduction of compressed‐air pressure and volume in vents, use of vibrating personal alarms instead of audible alarms	not reported		2 to 11 dB noise reduction					Maling 2016
Helicopter	Cover of structural leaks with lightweight materials (e.g. new door seals) and damping of the structure (patches of constrained visco‐elastic materials that are bonded to the structure), optimised sound‐proofing panels (sandwich panels with “soft core”) and windows (thickened laminated windows with damping layer and double glazing), and Main Gear Box suspension devices (laminated ball joints at MGB support strut foot)	not reported		7 dB noise reduction					Caillet 2012
Pump	Suppressor on palletizer hydraulic pump to minimize hydraulic banging, pump whine contained in sound‐insulated box	not reported	88 dB	83 dB					Morata 2015
Air‐rotary drill rig	Installation of hydraulic noise suppressors and a lead‐fiberglass blanket covering Ihe gap between the inside door and the cab frame	not reported	98 dB	95 dB			MSHA PEL 280%; NIOSH 3222%	MSHA PEL 210%: NIOSH 2585%
Air‐rotary drill rig	Installation of hydraulic noise suppressors	not reported	98 dB	97 dB			MSHA PEL 280%; NIOSH 3222%	MSHA PEL 249%; NIOSH 2951%
Pumps	Installing mufflers on pumps	not reported	98.1 dB	81.3 dB
Haul trucks in underground metal/non‐metal mines	Improving the engine compartment noise barrier: the usual barrier material has been replaced with a barrier material part number Duracote 5356, manufactured by Durasonic	not reported					MSHA PEL 495%	MSHA PEL 416%	Thompson 2015
Chiller	Reduce noise from a chiller with a combination of acoustic absorbent and retro‐fit constrained layer damping	not reported		8 dB noise reduction					Wilson 2016
High‐speed strip‐fed press	Normally the press legs are welded boxes, the press frame was isolated from the fabricated legs by inserting 6 mm composite pads between frame and legs	not reported			101 dB	92 dB			Wilson 2016
Product impact on hoppers and chutes	Coated internally with food‐grade, sound‐deadening material	not reported	96–98 dB	Noise reduced by 2‐8 dB					HSE 2013
Gas cylinder impact on metal table	Rubber matting on table	not reported	110 dB peaks	removal of peak noises
Product impact on ducting	Lagged ductwork with noise‐absorbent padding	not reported	92 dB	84 dB
Product impact on vibrating components	Coated externally with sound‐deadening material	not reported	92 dB	84 dB
Bread‐basket stacking machine	Fitted hydraulic dampers	not reported	92 dB	83 dB
Hand‐crimping metal foil packages	Mounted on layers of rubber	not reported	86–89 dB	85–86 dB
Keg impact on concrete floor	Fitted rubber matting on to floor	not reported	High noise levels	Noise levels reduced
Gas cylinder impact on metal ‘A’ frame trolleys	Fitted rubber matting on to trolleys	not reported	110 dB peaks	Peak noise levels reduced
Road tanker degassing	Fitted silencers	not reported	92 dB	83 dB
Evaporative condensers and refrigeration plant	Fitted silencers	not reported	94 dB	83–87 dB
	Number of cases: 20		mean before		mean after		mean reduction
	noise level dB		93.6		86.5		7
	TWA dB		101		92		9
	Dose % (MSHA PEL) [dosimeter settings: 90 dB Lt, 90 dB Lc, 5‐dB exchange rate]		351.7		291.7		60
	Dose % (NIOSH) [dosimeter settings: 80 dB Lt, 85 dB Lc, 3‐dB exchange rate]		3222		2768		454
MSHA = Mine safety and health administration NIOSH = National Institute for Occupational Safety and Health PEL = permissible exposure limit

Table 7. Results case studies ‐ damping material and silencers

Table 8. Results case studies ‐ design changes

Design changes
Noise source	Intervention	Follow‐up	Initial noise level	Noise level after	8 h TWA before	8 h TWA after	Dose before	Dose after	Reference ID
Roof bolting machine at underground coal mines	New drill bit isolator	immediate				reduced by 3.2 dB	MSHA PEL per hole 0.85%	MSHA PEL per hole 0.57%	Azman 2012
Roof bolting machine at underground coal mines	New drill bit isolator	short term (after 253 holes and 628 m)				reduced by 2.2 dB	MSHA PEL per hole 0.9%	MSHA PEL per hole 0.66%	Azman 2012
4‐roll calender in a tire manufacturing facility "calender operator"	Replacing the piercer brackets, optimising alignment and improving preventative maintenance (increased and more frequent lubrication of the piercer and other areas of the equipment with high friction or pressure)	not reported			87.7 dB	86.3 dB	OSHA dose 72.8%	OSHA dose 59.6%	Cockrell 2015
4‐roll calender in a tire manufacturing facility "wind up operator"	Replacing the piercer brackets, optimising alignment and improving preventative maintenance (increased and more frequent lubrication of the piercer and other areas of the equipment with high friction or pressure)	not reported			93.1 dB	89 dB	OSHA dose 153%	OSHA dose 87.3%	Cockrell 2015
Heavy metal arms which drove the reciprocating blade on the machines	Alternative linkage using flexible nylon straps	not reported	95 dB	75 dB					HSE 2015
Tobacco filter making machine	Machine design improvements on a tobacco filter making machine and room improvements	not reported		9 dB reduction					Maling 2016
Weaving machines	Use of different spindle	not reported	100 dB	90 dB					Maling 2016
Locomotive for mining	Active noise control	immediate							Pan 2016
Mining truck	Active noise control	immediate
Mining truck	active noise control and damping material	immediate
Filler	Filler outfeed: line shaft removed, individual drives installed	not reported	107 dB	81 dB					Morata 2015
Con‐air dryer	Machine set on vibration mounts, quieter blower	not reported	94 dB	85 dB
Transfer cart	not reported	not reported	94 dB	79 dB
Trimmer	rReplacing nozzles from trimmer with in feed decline drive belt	not reported	98 to 113 dB	86 to 104 dB
Continuous mining machine	Exchange of a single sprocket chain for a dual sprocket chain on a continuous mining machine (CMM, Joy Mining Machine 14CM‐15)	not reported			93.4 to 93.3 dB	92 dB	MSHA PEL 159 %	MSHA PEL 132.5%
Moen case former	Exchange of pneumatic cylinder for servo‐mandrel	not reported	97 dB	87 dB
Cart	Exchange of cart wheels	not reported	88 dB	72 dB
Standard longwall cutting drums (mining)	Modified set of longwall cutting drums instead of a set of standard (baseline) drums	not reported	98 dB	92 dB	95.7 dB	93.1 dB	MSHA PEL 220.5%	MSHA PEL 158.6%	Thompson 2015
Haul trucks in underground metal/non‐metal mines	Improving the engine compartment noise barrier and changing the fan type, size, and rotation speed (larger fan of different design and different fan pulley to reduce the fan rotation speed to 90%)	not reported			102 dB	93 dB	MSHA PEL 495%	MSHA PEL 158%
Load‐haul‐dumps (LHDs) in underground metal/non‐metal mines	Improving the engine compartment noise barrier and changing the fan type, size, and rotation speed (larger fan of a different design and a different fan hub to reduce the fan rotation speed to roughly 87% and new noise barrier material (Duracote Durasonic 5356))	not reported			98 dB	96 dB	MSHA PEL 289%	MSHA PEL 231%
Load‐haul‐dumps (LHDs) in underground metal/non‐metal mines	Improving the engine compartment noise barrier and changing the fan type, size, and rotation speed (a larger fan of a different design was installed as well as a different fan hub to reduce the fan rotation speed to roughly 95%)	not reported			98 dB	93 dB	MSHA PEL 289%	MSHA PEL 142%
Standard camshaft washer drying nozzles (pneumatic)	Pneumatic nozzles replaced with suitable entraining units	not reported		12 dB reduction					Wilson 2016
Drier fan	Retro‐fitting aerodynamic and acoustic elements inside fan casings and the associated ductwork	not reported		9 dB reduction
Aluminium can extract and chopper fans	Fitting aerodynamic inserts inside the fan casing	not reported		22 dB reduction
Separator (large thin sheet distribution dome)	alteration to a vibratory separator: forming this component in stainless sound deadened steel	not reported	105 dB	89 dB
Metal trays	Replacing metal trays with plastic trays	not reported	89 dB	84‐85 dB					HSE 2013
Metal wheels on baking racks	Replacing baking rack wheels with resin wheels	not reported	above 100 dB	86‐92 dB
Loosening product from baking tins with air knives	Air knives modified to operate with a diffuse air jet	not reported	above 90 dB	below 85 dB
Bottles and cans banging together on conveyors	Fitted a pressureless combiner conveyor system	not reported	above 90 dB	below 90 dB
Baking tins banging together on chain or slat conveyors	Installing ‘tin‐friendly’ conveyors	not reported	above 90 dB	below 85 dB
Manual changeover of baking tins on conveyor	Installed robots to handle pans	not reported	94‐96 dB	below 90 dB
Water pumps on filling machines	Replaced with air pumps and fitted silencers	not reported	90 dB	84 dB
Filling sachets and cups	New design of horizontal powder‐feeder and enclosed machine	not reported	83‐84 dB	80 dB
Bottle manufacture, filling and packing lines	Acoustic panels fitted to walls, high ceiling installed	not reported	Above 90 dB	83 dB
Contact between metal trays and metal tracking	Replaced with plastic tracking	not reported	94 dB	87 dB
Product impact on metal chutes	Replaced with plastic chutes	not reported	96‐98 dB	90 dB
Electrically powered sausage‐spooling machines	Replaced with compressed‐air spooler	not reported	86‐90 dB	below 80 dB
Tray‐indexing arm	Plastic caps on fingers of indexing arm	not reported	94 dB	87‐89 dB
Vibratory conveyor	Ensured conveyor only used at least noisy speed	not reported	above 90 dB	below 85
Glass bottles on conveyor	New design of conveyor with different chain speeds	not reported	101 dB	84 dB
Lidding and de‐lidding tins	Installed robots to lid and de‐lid baking tins	not reported	90‐93 dB	88 dB
	Number of cases: 41		mean before		mean after		mean reduction
	Noise level dB		94.5 dB		85.3 dB		9.6 dB
	TWA dB		95.4		91.8		3.4 dB
	Dose % (OSHA)		112.9		73.5		39.5
	Dose % (MSHA PEL)		207.8		117.6		90.1
MSHA = Mine Safety and Health Administration OSHA = Occupational Safety and Health Administration PEL = permissible exposure limit

Table 8. Results case studies ‐ design changes

Table 9. Results case studies ‐ enclosure

Enclosure
Noise source	Intervention	Follow‐up	Initial noise level	Noise level after	Reference ID
Conveyor	An enclosure was put over the conveyor at a cost of GBP 2000 and the conveyor speed was changed to reduce jar clashing	not reported	96 dB	86 dB	HSE 2015
Grinder	Enclosure over the grinder	not reported	93 dB	85 dB	Morata 2015
Not reported	Use of an enclosure with acoustical foam to deburring area	not reported	104 dB	82 dB	Morata 2015
Feeder	Enclosing the bowl feeder	not reported	116 dB	86 dB	Maling 2016
Compressed‐air knives	Enclosed machine	not reported	91–92 dB	Below 85 dB	HSE 2013
Glass‐bottle conveyor	Enclosed the conveyor noise levels	not reported	Above 90 dB	reduced by 2‐8 dB
Blower machine	Enclosed machine using sound‐absorbent panels	not reported	above 90	Below 90 dB
Bottle‐blowing machines	Machine enclosed and segregated	not reported	94 dB	89 dB
Hammer mill	Enclosed in an acoustic booth	not reported	102 dB	87 dB
Rinser‐filler‐capper machine	Enclosed machine	not reported	85 dB	73 dB
Glass jars clashing together on conveyor	Fitted enclosure and changed conveyor speed	not reported	96 dB	86 dB
Bottles banging together on filler infeed conveyor	Fitted covers over conveyor	not reported	96‐100 dB	92 dB
	Number of cases: 12		mean before	mean after	mean reduction
	Noise level (dB)		96.3 dB	85.5 dB	11.8 dB

Table 9. Results case studies ‐ enclosure

Table 10. Results case studies ‐ maintenance

Maintenance
Noise source	Intervention	Follow‐up	Initial noise level	Noise level after	Reference ID
Dough mixer	Maintenance modifications to a mixing machine	not reported	94 dB	91 dB	HSE 2013
Compressed air in soft drinks factory machines	Regular maintenance of machines to reduce noise from air leaks	not reported	High noise levels	Noise levels reduced by 3 to 4 dB
Gearboxes on mixing machine	Lubricating gearboxes	not reported	80–85 dB	Noise levels reduced by 1.5 dB
Compressed‐air exhausts on vacuum‐wrapping machines	Fitting and maintaining silencers on wrapping machines	not reported	88–90 dB	Below 85 dB
	Number of cases: 4		mean before	mean after	mean reduction
	Noise level dB		88.5 dB	85.7 dB	3 dB

Table 10. Results case studies ‐ maintenance

Table 11. Results case studies ‐ segregation

Segregation
Noise source	Intervention	Follow‐up	Initial noise level	Noise level after	Reference ID
Main production area of bakery	Re‐routing pedestrian traffic, signage and training	not reported	94 dB	below 85 dB	HSE 2013
Bowl chopper and mincers	Moved from main production area to an isolated area	not reported	88–94 dB	below 85 dB
Basket‐washing machine in main bakery	Moved to a separate building	not reported	88 dB	Noise source removed
High‐pressure air‐compressor	Located in a separate room	not reported	110–112 dB	60–70 dB outside room
Vibrating cap‐hoppers	Located in separate enclosure	not reported	Above 90 dB	Noise source removed
Air‐compressor	Located in separate, unmanned room	not reported	94–95 dB	80 dB
Pet food processing area	Solid block wall with acoustic panelling between processing and packaging area	not reported	95 dB	Below 85 dB
	Number of cases: 7		mean before	mean after	mean reduction
	Noise level dB		97.1 dB	80.0 dB	17.1 dB

Table 11. Results case studies ‐ segregation

Table 12. Risk of bias of interrupted time‐series

Study	Independence other changes	Sufficient data points	Formal test for trend	Intervention does not affect data	Blinded assessment of outcome	Complete data set	Reliable outcome measure
Joy 2007	Not done	Done	Done	Not done	Not done	Not clear	Done
Rabinowitz 2011	Not done	Done	Done	Done	Not Done	Done	Done

Table 12. Risk of bias of interrupted time‐series

Comparison 1. Legislation to decrease noise exposure (long‐term) ‐ ITS

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 Immediate change in level Show forest plot	1		immediate change in level (Random, 95% CI)	Totals not selected

1.1 Surface noise Intervention (Int) Year 1999	1		immediate change in level (Random, 95% CI)	0.0 [0.0, 0.0]
1.2 Underground noise Int Year 1999	1		immediate change in level (Random, 95% CI)	0.0 [0.0, 0.0]
1.3 Surface noise Int Year 2000	1		immediate change in level (Random, 95% CI)	0.0 [0.0, 0.0]
1.4 Underground noise Int Year 2000	1		immediate change in level (Random, 95% CI)	0.0 [0.0, 0.0]
2 Change in slope Show forest plot	1		change in slope (Random, 95% CI)	Totals not selected

2.1 Surface noise Int Year 1999	1		change in slope (Random, 95% CI)	0.0 [0.0, 0.0]
2.2 Underground noise Int Year 1999	1		change in slope (Random, 95% CI)	0.0 [0.0, 0.0]
2.3 Surface noise Int Year 2000	1		change in slope (Random, 95% CI)	0.0 [0.0, 0.0]
2.4 Underground noise Int Year 2000	1		change in slope (Random, 95% CI)	0.0 [0.0, 0.0]

Comparison 1. Legislation to decrease noise exposure (long‐term) ‐ ITS

Comparison 2. HPD (muffs) with instructions vs without instructions (immediate) ‐ RCT

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 Noise attenuation at 0.5 kHz (REAT) Show forest plot	1	40	Mean Difference (IV, Random, 95% CI)	2.34 [‐0.85, 5.54]

1.1 Wilson Sound Ban cap	1	20	Mean Difference (IV, Random, 95% CI)	4.1 [‐2.47, 10.67]
1.2 Bilsom UF‐1 muff	1	20	Mean Difference (IV, Random, 95% CI)	1.80 [‐1.86, 5.46]
2 Noise attenuation at 1 kHz (REAT) Show forest plot	1	40	Mean Difference (IV, Random, 95% CI)	0.89 [‐3.02, 4.80]

2.1 Wilson Sound Ban Cap	1	20	Mean Difference (IV, Random, 95% CI)	3.80 [‐3.70, 11.30]
2.2 Bilsom UF‐1 Muff	1	20	Mean Difference (IV, Random, 95% CI)	‐0.20 [‐4.78, 4.38]
3 Noise attenuation at 2 kHz (REAT) Show forest plot	1	40	Mean Difference (IV, Random, 95% CI)	2.57 [‐0.23, 5.38]

3.1 Wilson Sound Ban Cap	1	20	Mean Difference (IV, Random, 95% CI)	2.70 [‐1.89, 7.29]
3.2 Bilsom UF‐1 Muff	1	20	Mean Difference (IV, Random, 95% CI)	2.5 [‐1.05, 6.05]
4 Noise attenuation at 3 kHz (REAT) Show forest plot	1	40	Mean Difference (IV, Random, 95% CI)	2.23 [0.09, 4.36]

4.1 Wilson Sound Ban Cap	1	20	Mean Difference (IV, Random, 95% CI)	1.60 [‐3.01, 6.21]
4.2 Bilsom UF‐1 Muff	1	20	Mean Difference (IV, Random, 95% CI)	2.40 [‐0.01, 4.81]
5 Noise attenuation at 4 kHz (REAT) Show forest plot	1	40	Mean Difference (IV, Random, 95% CI)	0.83 [‐3.28, 4.95]

5.1 Wilson Sound Ban Cap	1	20	Mean Difference (IV, Random, 95% CI)	0.90 [‐6.18, 7.98]
5.2 Bilsom UF‐1 Muff	1	20	Mean Difference (IV, Random, 95% CI)	0.80 [‐4.26, 5.86]
6 Noise attenuation at 6 kHz (REAT) Show forest plot	1	40	Mean Difference (IV, Random, 95% CI)	0.64 [‐3.76, 5.04]

6.1 Wilson Sound Ban Cap	1	20	Mean Difference (IV, Random, 95% CI)	2.30 [‐7.31, 11.91]
6.2 Bilsom UF‐1 Muff	1	20	Mean Difference (IV, Random, 95% CI)	0.20 [‐4.75, 5.15]
7 Noise attenuation at 8 kHz (REAT) Show forest plot	1	40	Mean Difference (IV, Random, 95% CI)	1.14 [‐3.59, 5.87]

7.1 Wilson Sound Ban Cap	1	20	Mean Difference (IV, Random, 95% CI)	2.0 [‐8.13, 12.13]
7.2 Bilsom UF‐1 Muff	1	20	Mean Difference (IV, Random, 95% CI)	0.90 [‐4.45, 6.25]

Comparison 2. HPD (muffs) with instructions vs without instructions (immediate) ‐ RCT

Comparison 3. HPD (plugs) with instructions vs without instructions (immediate) ‐ RCT

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 Noise attenuation at 0.5 kHz (REAT) Show forest plot	1	40	Mean Difference (IV, Random, 95% CI)	12.69 [7.69, 17.69]

1.1 EAR foam plugs	1	20	Mean Difference (IV, Random, 95% CI)	16.30 [5.93, 26.67]
1.2 UltraFit plugs	1	20	Mean Difference (IV, Random, 95% CI)	11.6 [5.89, 17.31]
2 Noise attenuation at 1 kHz (REAT) Show forest plot	1	40	Mean Difference (IV, Random, 95% CI)	13.31 [8.13, 18.50]

2.1 EAR foam plugs	1	20	Mean Difference (IV, Random, 95% CI)	15.40 [5.62, 25.18]
2.2 UltraFit plugs	1	20	Mean Difference (IV, Random, 95% CI)	12.5 [6.39, 18.61]
3 Noise attenuation at 2 kHz (REAT) Show forest plot	1	40	Mean Difference (IV, Random, 95% CI)	9.62 [4.52, 14.72]

3.1 EAR foam plugs	1	20	Mean Difference (IV, Random, 95% CI)	7.90 [‐1.21, 17.01]
3.2 UltraFit plugs	1	20	Mean Difference (IV, Random, 95% CI)	10.40 [4.25, 16.55]
4 Noise attenuation at 3 kHz (REAT) Show forest plot	1	40	Mean Difference (IV, Random, 95% CI)	6.71 [2.66, 10.76]

4.1 EAR foam plugs	1	20	Mean Difference (IV, Random, 95% CI)	6.20 [‐1.54, 13.94]
4.2 UltraFit plugs	1	20	Mean Difference (IV, Random, 95% CI)	6.90 [2.15, 11.65]
5 Noise attenuation at 4 kHz (REAT) Show forest plot	1	40	Mean Difference (IV, Random, 95% CI)	7.97 [3.60, 12.34]

5.1 EAR foam plugs	1	20	Mean Difference (IV, Random, 95% CI)	6.00 [‐1.23, 13.23]
5.2 UltraFit plugs	1	20	Mean Difference (IV, Random, 95% CI)	9.10 [3.62, 14.58]
6 Noise attenuation at 6 kHz (REAT) Show forest plot	1	40	Mean Difference (IV, Random, 95% CI)	12.13 [6.21, 18.05]

6.1 EAR foam plugs	1	20	Mean Difference (IV, Random, 95% CI)	9.2 [‐1.87, 20.27]
6.2 UltraFit plugs	1	20	Mean Difference (IV, Random, 95% CI)	13.3 [6.30, 20.30]
7 Noise attenuation at 8 kHz (REAT) Show forest plot	1	40	Mean Difference (IV, Random, 95% CI)	11.07 [4.51, 17.64]

7.1 EAR foam plugs	1	20	Mean Difference (IV, Random, 95% CI)	7.60 [‐0.97, 16.17]
7.2 UltraFit plugs	1	20	Mean Difference (IV, Random, 95% CI)	14.3 [6.11, 22.49]
8 Mean noise attenuation over 0.5, 1, 2, 3, 4, 6, 8 kHz (REAT) Show forest plot	2	140	Mean Difference (IV, Fixed, 95% CI)	8.59 [6.92, 10.25]

8.1 Moldex Comets, EN352, USA	1	100	Mean Difference (IV, Fixed, 95% CI)	8.34 [6.58, 10.10]
8.2 EAR foam plugs	1	20	Mean Difference (IV, Fixed, 95% CI)	9.8 [0.60, 19.00]
8.3 UltraFit plugs	1	20	Mean Difference (IV, Fixed, 95% CI)	11.16 [4.87, 17.45]

Comparison 3. HPD (plugs) with instructions vs without instructions (immediate) ‐ RCT

Comparison 4. HPD (plugs) lower noise reduction rate (NRR) with instructions vs higher NRR without instructions (immediate) ‐ RCT

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 Mean attenuation at 0.5, 1, 2, 3, 4, 6, 8 kHz Show forest plot	1		Mean Difference (IV, Fixed, 95% CI)	Subtotals only

1.1 NRR 20 vs NRR 30	1	100	Mean Difference (IV, Fixed, 95% CI)	2.62 [1.75, 3.49]

Comparison 4. HPD (plugs) lower noise reduction rate (NRR) with instructions vs higher NRR without instructions (immediate) ‐ RCT

Comparison 5. HPD with ANC vs without ANC (immediate)

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 Noise attenuation (dB) Show forest plot	1	4	Mean Difference (IV, Fixed, 95% CI)	0.0 [0.0, 0.0]

1.1 Alpha‐200 series with Active Noise Cancelling	1	2	Mean Difference (IV, Fixed, 95% CI)	0.0 [0.0, 0.0]
1.2 Gentex/Bose Active Noise Cancelling	1	2	Mean Difference (IV, Fixed, 95% CI)	0.0 [0.0, 0.0]
2 TTS at 1 kHz (before exposure ‐ after exposure ) Show forest plot	1		Mean Difference (IV, Random, 95% CI)	Subtotals only

3 TTS at 2 kHz (before exposure ‐ after exposure ) Show forest plot	1		Mean Difference (IV, Random, 95% CI)	Subtotals only

4 TTS at 4 kHz (before exposure ‐ after exposure ) Show forest plot	1		Mean Difference (IV, Random, 95% CI)	Subtotals only

5 TTS at 6 kHz (before exposure ‐ after exposure ) Show forest plot	1		Mean Difference (IV, Random, 95% CI)	Subtotals only

6 TTS at 8 kHz (before exposure ‐ after exposure ) Show forest plot	1		Mean Difference (IV, Random, 95% CI)	Subtotals only

Comparison 5. HPD with ANC vs without ANC (immediate)

Comparison 6. Custom‐moulded musician HPD (plugs) with higher versus HPD (plugs) with lower noise attenuation

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 Noise attenuation dB(A) Show forest plot	1	20	Mean Difference (IV, Random, 95% CI)	3.10 [1.12, 5.08]

Comparison 6. Custom‐moulded musician HPD (plugs) with higher versus HPD (plugs) with lower noise attenuation

Comparison 7. HPD (various) noise attenuation (immediate)

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 Noise attenuation (dB) Show forest plot	1	36	Mean Difference (IV, Fixed, 95% CI)	0.0 [0.0, 0.0]

1.1 Peltor H61 Muff Elec	1	6	Mean Difference (IV, Fixed, 95% CI)	0.0 [0.0, 0.0]
1.2 Peltor H7 Muff Elec	1	6	Mean Difference (IV, Fixed, 95% CI)	0.0 [0.0, 0.0]
1.3 Peltor H6 Muff Elec	1	6	Mean Difference (IV, Fixed, 95% CI)	0.0 [0.0, 0.0]
1.4 Bilsom Marksman Muff Elec	1	6	Mean Difference (IV, Fixed, 95% CI)	0.0 [0.0, 0.0]
1.5 Silenta Hunter Muff Elec	1	6	Mean Difference (IV, Fixed, 95% CI)	0.0 [0.0, 0.0]
1.6 EAR Ultra 9000 Plug	1	6	Mean Difference (IV, Fixed, 95% CI)	0.0 [0.0, 0.0]

Comparison 7. HPD (various) noise attenuation (immediate)

Comparison 8. HLPP with noise level indicator vs no noise level indicator

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 Change in noise levels at 2 months' follow‐up Show forest plot	1	132	Mean Difference (IV, Random, 95% CI)	0.32 [‐2.44, 3.08]

1.1 Extensive information plus NLI vs information only	1	64	Mean Difference (IV, Random, 95% CI)	‐0.40 [‐4.37, 3.57]
1.2 Information plus NLI vs Information only	1	68	Mean Difference (IV, Random, 95% CI)	1.0 [‐2.84, 4.84]
2 Change in noise levels at 4 months' follow‐up Show forest plot	1	132	Mean Difference (IV, Fixed, 95% CI)	‐0.14 [‐2.66, 2.38]

2.1 Extensive information plus NLI vs information only	1	64	Mean Difference (IV, Fixed, 95% CI)	‐0.30 [‐3.95, 3.35]
2.2 Information plus NLI vs information only	1	68	Mean Difference (IV, Fixed, 95% CI)	0.0 [‐3.48, 3.48]

Comparison 8. HLPP with noise level indicator vs no noise level indicator

Comparison 9. HLPP with extensive information vs information only

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 Change in noise levels at 2 months' follow‐up Show forest plot	1		Mean Difference (IV, Fixed, 95% CI)	Totals not selected

2 Change in noise levels at 4 months' follow‐up Show forest plot	1		Mean Difference (IV, Random, 95% CI)	Totals not selected

Comparison 9. HLPP with extensive information vs information only

Comparison 10. V‐51‐R plug versus EAR plug (immediate)

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 TTS at 0.5 kHz (Hearing loss before exposure ‐ after exposure ) Show forest plot	1	70	Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]

1.1 After 8 minutes out of noise	1	18	Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]
1.2 After 14.6 minutes out of noise	1	18	Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]
1.3 After 20 minutes out of noise	1	17	Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]
1.4 After 27.2 minutes out of noise	1	17	Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]
2 TTS at 1 kHz (before exposure ‐ after exposure ) Show forest plot	1		Mean Difference (IV, Random, 95% CI)	Subtotals only

2.1 After 8 minutes out of noise	1	18	Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]
2.2 After 14.6 minutes out of noise	1	18	Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]
2.3 After 20 minutes out of noise	1	17	Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]
2.4 After 27.2 minutes out of noise	1	17	Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]
3 TTS at 2 kHz (before exposure ‐ after exposure ) Show forest plot	1		Mean Difference (IV, Random, 95% CI)	Subtotals only

3.1 After 8 minutes out of noise	1	18	Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]
3.2 After 14.6 minutes out of noise	1	18	Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]
3.3 After 20 minutes out of noise	1	17	Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]
3.4 After 27.2 minutes out of noise	1	17	Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]
4 TTS at 3 kHz (before exposure ‐ after exposure ) Show forest plot	1		Mean Difference (IV, Random, 95% CI)	Subtotals only

4.1 After 8 minutes out of noise	1	18	Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]
4.2 After 14.6 minutes out of noise	1	18	Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]
4.3 After 20 minutes out of noise	1	17	Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]
4.4 After 27.2 minutes out of noise	1	17	Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]
5 TTS at 4 kHz (before exposure ‐ after exposure) Show forest plot	1		Mean Difference (IV, Random, 95% CI)	Subtotals only

5.1 After 8 minutes out of noise	1	18	Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]
5.2 After 14.6 minutes out of noise	1	18	Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]
5.3 After 20 minutes out of noise	1	17	Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]
5.4 After 27.2 minutes out of noise	1	17	Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]
6 TTS at 6 kHz (before exposure ‐ after exposure) Show forest plot	1		Mean Difference (IV, Random, 95% CI)	Subtotals only

6.1 After 8 minutes out of noise	1	18	Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]
6.2 After 14.6 minutes out of noise	1	18	Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]
6.3 After 20 minutes out of noise	1	17	Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]
6.4 After 27.2 minutes out of noise	1	17	Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]

Comparison 10. V‐51‐R plug versus EAR plug (immediate)

Comparison 11. Earmuffs vs earplugs (long‐term)

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 Hearing loss change over 3 years (4 kHz / STS) Show forest plot	2		OR (Random, 95% CI)	Subtotals only

1.1 High noise exposure > 89 dB(A)	2		OR (Random, 95% CI)	0.80 [0.63, 1.03]
1.2 Low noise exposure < 89 dB(A)	2		OR (Random, 95% CI)	2.65 [0.40, 17.52]

Comparison 11. Earmuffs vs earplugs (long‐term)

Comparison 12. HLPP vs audiometric testing (agriculture students, long‐term, 3‐year and 16‐year follow‐up) ‐ RCT

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 STS Show forest plot	1		Odds Ratio (Fixed, 95% CI)	Subtotals only

1.1 3‐year follow‐up	1		Odds Ratio (Fixed, 95% CI)	0.85 [0.29, 2.44]
1.2 16‐year follow‐up	1		Odds Ratio (Fixed, 95% CI)	0.94 [0.46, 1.91]

Comparison 12. HLPP vs audiometric testing (agriculture students, long‐term, 3‐year and 16‐year follow‐up) ‐ RCT

Comparison 13. HLPP with daily noise‐exposure monitoring with feedback vs annual audiometry (long‐term) ‐ ITS

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 HL (dB/year at 2, 3 and 4 kHz) Δ level Show forest plot	1		rate of hearing loss (Random, 95% CI)	Totals not selected

1.1 intervention ‐ controlled for age, gender, baseline hearing	1		rate of hearing loss (Random, 95% CI)	0.0 [0.0, 0.0]
1.2 control ‐ controlled for age, gender, baseline hearing	1		rate of hearing loss (Random, 95% CI)	0.0 [0.0, 0.0]
1.3 intervention minus control ‐ controlled for age, gender, baseline hearing	1		rate of hearing loss (Random, 95% CI)	0.0 [0.0, 0.0]
1.4 intervention ‐ controlled for age, gender, baseline hearing and initial rate of HL	1		rate of hearing loss (Random, 95% CI)	0.0 [0.0, 0.0]
1.5 control ‐ controlled for age, gender, baseline hearing and initial rate of HL	1		rate of hearing loss (Random, 95% CI)	0.0 [0.0, 0.0]
1.6 intervention minus control ‐ controlled for age, gender, baseline hearing and initial rate of HL	1		rate of hearing loss (Random, 95% CI)	0.0 [0.0, 0.0]
2 HL (dB/year at 2, 3 and 4 kHz) slope Show forest plot	1		rate of hearing loss (Fixed, 95% CI)	Totals not selected

2.1 intervention ‐ controlled for age, gender, baseline hearing	1		rate of hearing loss (Fixed, 95% CI)	0.0 [0.0, 0.0]
2.2 control ‐ controlled for age, gender, baseline hearing	1		rate of hearing loss (Fixed, 95% CI)	0.0 [0.0, 0.0]
2.3 intervention minus control ‐ controlled for age, gender, baseline hearing	1		rate of hearing loss (Fixed, 95% CI)	0.0 [0.0, 0.0]
2.4 intervention ‐ controlled for age, gender, baseline hearing and initial rate of HL	1		rate of hearing loss (Fixed, 95% CI)	0.0 [0.0, 0.0]
2.5 control ‐ controlled for age, gender, baseline hearing and initial rate of HL	1		rate of hearing loss (Fixed, 95% CI)	0.0 [0.0, 0.0]
2.6 intervention minus control ‐ controlled for age, gender, baseline hearing and initial rate of HL	1		rate of hearing loss (Fixed, 95% CI)	0.0 [0.0, 0.0]

Comparison 13. HLPP with daily noise‐exposure monitoring with feedback vs annual audiometry (long‐term) ‐ ITS

Comparison 14. Follow‐up exam after initial STS vs no exam (long‐term)

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 Hearing loss change (STS) Show forest plot	1	1317	Odds Ratio (M‐H, Fixed, 95% CI)	0.87 [0.56, 1.36]

Comparison 14. Follow‐up exam after initial STS vs no exam (long‐term)

Comparison 15. Well‐implemented HLPP vs less well‐implemented (long‐term, 1‐year follow‐up)

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 STS Show forest plot	1	341	Risk Ratio (M‐H, Fixed, 95% CI)	0.36 [0.09, 1.42]

Comparison 15. Well‐implemented HLPP vs less well‐implemented (long‐term, 1‐year follow‐up)

Comparison 16. Well‐implemented HLPP vs less well‐implemented (long‐term > 5‐year follow‐up)

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 Hearing loss change STS/at 4 kHz Show forest plot	3	16301	OR (Random, 95% CI)	0.40 [0.23, 0.69]

1.1 Adera 2000	1	15345	OR (Random, 95% CI)	0.26 [0.14, 0.47]
1.2 Adera 1993	1	692	OR (Random, 95% CI)	0.35 [0.19, 0.65]
1.3 Brink 2000	1	264	OR (Random, 95% CI)	0.62 [0.40, 0.97]

Comparison 16. Well‐implemented HLPP vs less well‐implemented (long‐term > 5‐year follow‐up)

Comparison 17. HLPP 12‐hour shift vs HLPP 8‐hour shift (long‐term 1‐year follow‐up)

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 Hearing loss change over 1 year at 4 kHz Show forest plot	1		Mean Difference (IV, Fixed, 95% CI)	Totals not selected

Comparison 17. HLPP 12‐hour shift vs HLPP 8‐hour shift (long‐term 1‐year follow‐up)

Comparison 18. HLPP vs non‐exposed workers (long‐term 1‐year follow‐up)

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 hearing loss STS Show forest plot	1		Risk Ratio (Random, 95% CI)	3.38 [1.23, 9.32]

1.1 low‐exposed engineers	1		Risk Ratio (Random, 95% CI)	2.07 [0.27, 15.99]
1.2 medium‐exposed infantry	1		Risk Ratio (Random, 95% CI)	2.82 [0.37, 21.57]
1.3 high‐exposed artillery	1		Risk Ratio (Random, 95% CI)	4.69 [1.13, 19.51]

Comparison 18. HLPP vs non‐exposed workers (long‐term 1‐year follow‐up)

Comparison 19. Improved HLPP vs non‐exposed workers (long‐term 1‐year follow‐up)

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 hearing loss STS Show forest plot	1		Risk Ratio (Fixed, 95% CI)	Totals not selected

1.1 high‐exposed artillery	1		Risk Ratio (Fixed, 95% CI)	0.0 [0.0, 0.0]

Comparison 19. Improved HLPP vs non‐exposed workers (long‐term 1‐year follow‐up)

Comparison 20. HLPP vs non‐exposed workers (long‐term > 5‐year follow‐up)

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 Hearing loss change at 4 kHz/STS (5‐year follow‐up) Show forest plot	4	2231	effect size (Fixed, 95% CI)	0.05 [‐0.05, 0.16]

1.1 Pell hearing loss 10 dB	1	628	effect size (Fixed, 95% CI)	‐0.1 [‐0.27, 0.07]
1.2 Pell hearing loss 15 to 35 dB	1	559	effect size (Fixed, 95% CI)	0.09 [‐0.11, 0.29]
1.3 Pell hearing loss 40 dB	1	385	effect size (Fixed, 95% CI)	0.18 [‐0.06, 0.42]
1.4 Lee‐Feldstein	1	474	effect size (Fixed, 95% CI)	0.29 [‐0.07, 0.66]
1.5 Hager	1	43	effect size (Fixed, 95% CI)	‐0.1 [‐0.72, 0.52]
1.6 Gosztonyi	1	142	effect size (Fixed, 95% CI)	0.15 [‐0.18, 0.48]
2 Hazard of STS Show forest plot	1		Hazard Ratio (Random, 95% CI)	3.78 [2.69, 5.31]

2.1 80 to 85 dB‐years	1		Hazard Ratio (Random, 95% CI)	2.10 [1.26, 3.49]
2.2 85 to 90 dB‐years	1		Hazard Ratio (Random, 95% CI)	3.00 [2.27, 3.96]
2.3 90 to 95 dB‐years	1		Hazard Ratio (Random, 95% CI)	3.30 [2.76, 3.94]
2.4 95 to 100 dB‐years	1		Hazard Ratio (Random, 95% CI)	4.60 [3.86, 5.48]
2.5 More than 100 dB‐years	1		Hazard Ratio (Random, 95% CI)	6.60 [5.56, 7.84]

Comparison 20. HLPP vs non‐exposed workers (long‐term > 5‐year follow‐up)

Comparison 21. HLPP vs non‐exposed sensitivity analysis (long‐term, 5‐year follow‐up)

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 Hearing loss change at 4kHz / STS Show forest plot	3		effect size (Fixed, 95% CI)	0.17 [‐0.06, 0.40]

1.1 Lee‐Feldstein	1		effect size (Fixed, 95% CI)	0.29 [‐0.07, 0.66]
1.2 Hager	1		effect size (Fixed, 95% CI)	‐0.1 [‐0.72, 0.52]
1.3 Gosztonyi	1		effect size (Fixed, 95% CI)	0.15 [‐0.18, 0.48]

Comparison 21. HLPP vs non‐exposed sensitivity analysis (long‐term, 5‐year follow‐up)