4.3.3. Assessment of risk of bias in included studies

We assessed the risk of bias at the study level by using the Cochrane Risk of Bias tool (Higgins, 2011a). For non‐randomised designs, we used the ‘Risk of Bias’ tool from the Cochrane Effective Practice and Organisation of Care Group (EPOC, 2009) with some modifications. The tool used covers allocation sequence, the similarity of baseline outcome measurement, the similarity of baseline characteristics, incomplete outcome data, blinding of allocation, protection against contamination, selective outcome reporting, and other risks of bias. We prepared a risk of bias table that includes both RCTs (and/or non‐RCTs and/or controlled before‐after (CBA) studies) and interrupted time series (ITS) studies in Review Manager 5.4.1 (RevMan Web, 2019), as suggested in Risk of Bias Criteria for EPOC reviews (EPOC, 2017b). The two review authors (HHA, CN) independently assessed the risk of bias. For most of the items, we rated them as ‘yes’ (low risk of bias), ‘no’ (high risk of bias), or ‘unclear’ (unclear risk of bias) to make judgements of risk of bias.

Two investigators independently evaluated all eligible studies, where the Cohen's κ 0.86 indicated perfect agreement. Discrepancies were settled by consensus and consulted a third investigator of the team (DKC) if needed.

We presented an overall grading of the evidence related to each of the main outcomes using the GRADE (Grades of Recommendation, Assessment, Development, and Evaluation) approach. The GRADE approach defines the quality of a body of evidence as to the extent to which one can be confident that an estimate of effect or association is close to the true quantity of specific interest. The quality of a body of evidence involves the consideration of the risk of bias within a trial (methodological quality), the directness of evidence, heterogeneity, the precision of effect estimates, and the risk of publication bias (Schünemann, 2011). A level of evidence for the ‘body of evidence’ is assigned, ranging from high, moderate, low to very low, as part of the GRADE process (Atkins, 2004). We did not exclude studies on the grounds of risk of bias, but sources of bias were reported when presenting the results of studies. We presented all included studies and provided a narrative discussion on the risk of bias together with the potential limitations of the review as well as implications of bias in the interpretation of the results under the ‘Discussion’ section of the full‐text review.