Analysis of risk of bias assessments in a sample of intervention systematic reviews, Part II: focus on risk of bias tools reveals few meet current appraisal standards

Objectives

Risk of bias (RoB) assessment is a critical part of any systematic review (SR). There are multiple tools available for assessing RoB of the studies included in a SR. The conduct of these assessments in intervention SRs are addressed by three items in AMSTAR-2, considered the preferred tool for critically appraising an intervention SR. This study focuses attention on item 9, which assesses the ability of a RoB tool to adequately address sources of bias, particularly in randomized trials (RCTs) and nonrandomized studies of interventions (NRSI). Our main objective is to report the detailed results of our examination of both Cochrane and non-Cochrane RoB tools and distinguish those that meet AMSTAR-2 item 9 appraisal standards.

Study Design and Setting

We identified critical appraisal tools reported in a sample of 126 SRs reporting on interventions for persons with cerebral palsy published from 2014 to 2021. Eligible tools were those that had been used to assess the primary studies included in these SRs and for which assessment results were reported in enough detail to allow appraisal of the tool. We identified the version of the tool applied as original, modified, or novel and established the applicable study designs as intended by the tools’ developers. We then evaluated the potential ability of these tools to assess the four sources of bias specified in AMSTAR-2 item 9 for RCTs and NRSI. We adapted item 9 to appraise tools applied to single-case experimental designs, which we also encountered in this sample of SRs.

Results

Most of the eligible tools are recognized by name in the published literature and were applied in the original or modified form. Modifications were applied with considerable variability across the sample. Of the 37 tools we examined, those judged to fully meet the appraisal standards for RCTs included all the Cochrane tools, the original and modified Downs and Black Checklist, and the quality assessment standard for a cross-over study by Ding et al; for NRSI, these included all the Cochrane tools, the original and modified Downs and Black Checklist, and the Research Triangle Institute item bank on Risk of Bias and Precision of Observational Studies for NRSI. In general, tools developed for a specific study design were judged to meet the appraisal standards fully or partially for that design. These results suggest it is unlikely that a single tool will be adequate by AMSTAR-2 item 9 appraisal standards for an intervention SR that includes studies of various designs.

Conclusion

To our knowledge, this is the first resource providing SR authors with practical information about the appropriateness and adequacy of RoB tools by the appraisal standards specified in AMSTAR-2 item 9 for RCTs and NRSI. We propose similar methods for appraisal of tools applied to single-case experimental design. We encourage authors to seek contemporary RoB tools developed for use in healthcare-related intervention SRs and designed to evaluate relevant study design features. The tools should address attributes unique to the review topic and research question but not be subjected to unjustified and excessive modifications. We promote recognition of the potential shortcomings of both Cochrane and non-Cochrane RoB tools, even those that perform well by AMSTAR-2 item 9 appraisal standards.