In an attempt to provide a standardised and reliable assessment of the quality of the evidence of the study outcomes, we decided to use the GRADE evidence profile, a systematic and explicit system for grading the evidence into four quality categories. We reported the results obtained through this approach in a 'Summary of findings' table”.

Methods for future updates

Two pre‐planned analysis were not performed due to insufficient data. These will be implemented, if possible, in future updates of the review.

Methods for analysing continuous data: the scales used to assess tremor in the majority of the studies are continuous. We will transform ordinal scales with enough categories to continuous scales by assigning a score to each grade so that we can express the intervention effect as a difference in means or as a standardised mean difference. In the case of an ordinal scale with few categories, we will combine data from adjacent categories into two categories, and use methods for binary data as risk ratios (RR) or risk differences (RD) to evaluate the intervention effect.

Sensitivity analysis: we will undertake sensitivity analyses to assess the robustness of results to fixed‐effect versus random‐effects assumptions, and the inclusion or exclusion of studies at high risk of bias (i.e. inadequate allocation concealment and lack of blinded outcome assessor). We will use best‐ and worst‐case scenarios for taking into account missing data.