Types of studies

Randomised controlled trials (including cluster‐randomised). If studies that use a cross‐over design are included, we will only include data from the first treatment phase. Quasi‐randomised controlled studies will not be included.

We will apply no restrictions on language, year of publication or publication status.

Types of participants

Participants will be at least 18 years of age with tinnitus as the primary reason for seeking treatment.

In the event that studies include an age range of participants below 18 years (e.g. 16 to 21 years), they will be included if the mean age is 18 years or above.

Types of interventions

The primary intervention of interest is CBT. For the purposes of this review we will include studies that also describe CBT interventions that apparently only use cognitive or behavioural elements. Interventions such as ACT and mindfulness will also be included but simply considered as types of CBT.

For the purposes of determining similarities for subgroup analysis, we will contact authors of studies that examine the effectiveness of an apparently 'pure' cognitive or behavioural interventions and request treatment manuals or protocols. Two authors will then independently review the intervention manual classifying treatment elements as either cognitive or behavioural. Based on results from a review of treatment components used in psychological therapy for people with tinnitus (Thompson 2016) and the behaviour change taxonomy (Michie 2013), we will classify interventions as either 'cognitive only', 'behavioural only' or 'CBT'. In the event that the review authors differ in their judgements, a third review author will act as an arbiter.

We will stratify studies into four comparisons:

• CBT versus no intervention/waiting list control;

• CBT versus usual audiological care (tinnitus education and rehabilitation for hearing loss);

• CBT versus TRT (directive counselling and bilateral masking);

• CBT versus other experimental control (pooled if using the same experimental control). Other experimental controls may include transcranial magnetic stimulation, electrical or electromagnetic stimulation therapy and bio‐ neuro‐feedback.

Types of outcome measures

We will analyse the following outcomes in the review, but we will not use them as a basis for including or excluding studies.

Electronic searches

Published, unpublished and ongoing studies will be identified by searching the following databases from their inception:

• the Cochrane Register of Studies ENT Trials Register (search to date);

• Cochrane Register of Studies Online (search to date);

• Ovid MEDLINE (1946 to date);

  • Ovid MEDLINE (In‐Process & Other Non‐Indexed Citations);

  • PubMed (as a top up to searches in Ovid MEDLINE);

• Ovid EMBASE (1974 to date);

• EBSCO CINAHL (1982 to date);

• Ovid AMED (1985 to date);

• Ovid PsycINFO (1806 to date);

• Ovid CAB abstracts (1910 to date);

• LILACS (search to date);

• KoreaMed (search to date);

• IndMed (search to date);

• PakMediNet (search to date);

• Web of Knowledge, Web of Science (1945 to date);

• ClinicalTrials.gov, www.clinicaltrials.gov (search via the Cochrane Register of Studies to date);

• World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP) (search to date);

• ISRCTN, www.isrctn.com (search to date);

• Google Scholar (search to date).

The subject strategies for databases will be modelled on the search strategy designed for CENTRAL (Appendix 5). Where appropriate, these will be combined with subject strategy adaptations of the highly sensitive search strategy designed by Cochrane for identifying randomised controlled trials and controlled clinical trials (as described in the Cochrane Handbook for Systematic Reviews of Interventions Version 5.1.0, Box 6.4.b (Higgins 2011).

Searching other resources

We will scan the reference lists of identified publications for additional trials and contact trial authors if necessary. In addition, the Information Specialist will search Ovid MEDLINE, theCochrane Library and Google to retrieve existing systematic reviews relevant to this systematic review, so that we can scan their reference lists for additional trials.

Selection of studies

TF and RC will independently screen titles and abstracts from the search results for eligible studies. If there are disagreements at this screening stage, we will obtain copies of the full‐text articles and examine them closely for eligibility. For all disagreements over full‐text articles being assessed for inclusion, a third review author will be consulted as an arbiter.

We will record and present the flow of study identification and selection in the form of a PRISMA flow chart (Moher 2009).

Data extraction and management

TF will co‐ordinate the retrieval of full‐text articles as well as the management and extraction of all data. Two of TF, RC or BM will independently extract data from the included studies into standardised data forms based on a generic form developed by the Cochrane ENT editorial group. In the event that one of the review authors is the author of an included study he or she will not extract data from the study. Where relevant, review authors will be required to copy and paste verbatim text from included articles into the data extraction form. Any disagreements in the data extraction will first be addressed through discussion between the review authors involved. If that does not lead to agreement, a third review author will be consulted as an arbiter. In the event of information from an included study not being reported in adequate detail to enable decisions about inclusion or exclusion, we will contact the authors to request the provision of additional information.

Data extraction will include information on the following: details of the source, eligibility, methods, participants, intervention treatment elements, outcome measures at baseline (or pre‐test) and other time points reported in the respective studies, results including estimates of effects and confidence intervals, details of the funding source, key conclusions from the authors, comments from the review authors especially with regard to any differences between protocols and study reports, details of any correspondence required and any references to other relevant studies. Further details of the data to be extracted for intervention reviews are specified in table 7.2 of the Cochrane Handbook for Systematic of Interventions (Higgins 2011).

At the completion of data collection and once there is agreement on the data set that has been extracted, we will enter data into Review Manager 5.3 (RevMan 2014).

Assessment of risk of bias in included studies

TF and AW will undertake assessment of the risk of bias of the included trials independently, with the following taken into consideration, as guided by theCochrane Handbook for Systematic Reviews of Interventions (Higgins 2011):

• sequence generation;

• allocation concealment;

• blinding;

• incomplete outcome data;

• selective outcome reporting; and

• other sources of bias.

We will use the Cochrane 'Risk of bias' tool in RevMan 5.3 (RevMan 2014), which involves describing each of these domains as reported in the trial and then assigning a judgement about the adequacy of each entry: 'low', 'high' or 'unclear' risk of bias. In the event of disagreement between assessors of risk of bias, we will discuss the rationale for the respective judgements in an effort to resolve the differences. If this does not lead to agreement, a third review author will act as an arbiter.

Measures of treatment effect

We will analyse ordinal data as if it were continuous data and use standardised mean differences (SMD) and Cohen's d effect size measurement to estimate treatment effects for measures of tinnitus reactivity and other continuous measures of secondary outcomes. If feasible, we will also pool data from the same scale and use mean differences (MD). In the scenario where dichotomous data are reported we will analyse the data using risk ratios (RR) with 95% confidence intervals (95% CIs).

Unit of analysis issues

We do not anticipate that researchers conducting RCTs of CBT for tinnitus will employ a cross‐over design (i.e. where patients/participants receive both the experimental and control interventions) due to the carry over effects that would be expected from a CBT intervention. However, if an included study uses a cross‐over design individual participant data constituting the unit of analysis from the first treatment phase would be included in a meta‐analysis.

If any included study uses a cluster‐randomised design we will choose statistical methods in consultation with a statistician and following the recommendations in the Cochrane Handbook for Systematic Reviews of Interventions to "extract an estimate of the required effect measure from an analysis that accounts for the cluster design" using an odds ratio with confidence interval or generalised estimating equations (Higgins 2011). Also as specified we will use the inverse variance method to meta‐analyse effect estimates and standard errors so that the clustered nature of the data is taken into consideration (Higgins 2011).

Dealing with missing data

Whenever possible we will attempt to contact the investigators to request missing data relating to, for example, study characteristics, outcome measures, or how many patients dropped out or were included in the analysis. In relation to missing information about dropout or numbers included in the analysis, if we do not receive a response from the authors, we will conduct the analysis using a conservative approach and assume that the missing patients' data indicate no effect of/from the intervention. We will undertake a sensitivity analysis to examine the effect of this assumption by comparing the results with what would happen if the missing patients had the best possible outcome.

Where there are missing standard deviations for continuous data, we will use methods to estimate these using confidence intervals, standard errors, t, P or F values where reported.

We will record attempts to contact authors for missing data and responses (or otherwise) and, along with consideration of the potential impact of the missing data, report this in the Discussion section of the review.

Assessment of heterogeneity

We will investigate clinical heterogeneity with regard to: components of the interventions, mode of delivery, level of action, who delivers the CBT and the type of intervention used in the control condition. We will assess methodological heterogeneity according to study design and risk of bias (i.e. randomisation, blinding of outcome assessment, losses to follow‐up).

We will assess the degree of statistical heterogeneity that exists across studies using the I² statistic and we will use the following from the Cochrane Handbook for Systematic Reviews of Interventions as a guide for interpretation (Higgins 2011):

• 0% to 40%: might not be important;

• 30% to 60%: may represent moderate heterogeneity;

• 50% to 90%: may represent substantial heterogeneity;

• 75% to 100%: considerable heterogeneity.

Assessment of reporting biases

If we are able to include 10 or more studies, we will examine reporting bias through the creation of a funnel plot.

Data synthesis

In the event of being able to conduct meta‐analyses, we will use a random‐effects model as we expect that there will be differences between the study populations and methods used. We will subsequently conduct a sensitivity analysis using a fixed‐effect model.

First we will pool all studies if there is sufficient similarity between them with regard to: outcome (good convergent validity), level of action (i.e. individual or group therapy) and mode of delivery (i.e. in person, face‐to‐face or online). We assume that the included studies will all be RCTs, intervention studies and include a patient population.

We will stratify studies into four comparisons:

• CBT versus no intervention/waiting list control;

• CBT versus usual audiological care (tinnitus education and rehabilitation for hearing loss);

• CBT versus TRT (directive counselling and bilateral masking);

• CBT versus other experimental control (pooled if using the same experimental control). Other experimental controls may include transcranial magnetic stimulation, electrical or electromagnetic stimulation therapy or bio‐ neuro‐feedback.

The intention is to pool the results of the CBT treatments. However, if CBT treatment protocols are found to differ extensively synthesis may not be valid and we will conduct clustered analyses.

We will not pool studies if they differ on multiple clinical (intervention type, participant characteristics, mode of delivery, level of action, outcome) or methodological (study design, comparator) criteria relevant for a specific question the review addresses. Similarly, if there are indications of significant statistical heterogeneity (i.e. the I² statistic is > 30%, the Chi² value is greater than the degrees of freedom and/or the confidence intervals of the included studies do not show overlap), we will not pool studies and instead we will describe the findings in a narrative form.

Subgroup analysis and investigation of heterogeneity

We plan to conduct subgroup analyses for the primary outcome of tinnitus reactivity for the following:

• Studies by types of therapy: 'cognitive only', 'behavioural only', 'cognitive and behavioural only'.

• Studies by modes of delivery: 'face‐to‐face' or 'online CBT'.

• Studies by unit of delivery: 'individual patient therapy' or 'group therapy'.

• Study or patient groups by who delivers CBT; 'psychologists' or 'psychiatrists' or 'audiologists' or other therapists or clinicians.

• Studies by whether participants are included/excluded according to their hearing status: 'hearing loss was an exclusion criterion' or 'hearing loss was not an exclusion criterion'.

Sensitivity analysis

We plan to conduct the following sensitivity analyses to examine the role of:

• meta‐analysis using random‐effects and fixed‐effect models respectively;

• including or excluding studies at high risk of bias for incomplete outcome data.