Disagreements in risk of bias assessment for randomised controlled trials included in more than one Cochrane systematic reviews: A research on research study using cross-sectional design

Objectives Assess the frequency and reasons for disagreements in risk of bias assessments for randomised controlled trials (RCTs) included in more than one Cochrane review. Design Research on research study, using cross-sectional design. Data sources 2796 Cochrane reviews published between March 2011 and September 2014. Data selection RCTs included in more than one review. Data extraction Risk of bias assessment and support for judgement for five key risk of bias items. Data synthesis For each item, we compared risk of bias assessment made in each review and calculated proportion of agreement. Two reviewers independently analysed 50% of all disagreements by comparing support for each judgement with information from study report to evaluate whether disagreements were related to a difference in information (eg, contact the study author) or a difference in interpretation (same support for judgement but different interpretation). They also identified main reasons for different interpretation. Results 1604 RCTs were included in more than one review. Proportion of agreement ranged from 57% (770/1348 trials) for incomplete outcome data to 81% for random sequence generation (1193/1466). Most common source of disagreement was difference in interpretation of the same information, ranging from 65% (88/136) for random sequence generation to 90% (56/62) for blinding of participants and personnel. Access to different information explained 32/136 (24%) disagreements for random sequence generation and 38/205 (19%) for allocation concealment. Disagreements related to difference in interpretation were frequently related to incomplete or unclear reporting in the study report (83% of disagreements related to different interpretation for random sequence generation). Conclusions Risk of bias judgements of RCTs included in more than one Cochrane review differed substantially. Most disagreements were related to a difference in interpretation of an incomplete or unclear description in the study report. A clearer guidance on common causes of incomplete information may improve agreement.