Abstract
OBJECTIVE: To measure the frequency of adequate methods, inadequate methods and poor reporting in published randomised controlled trials (RCTs) and test potential factors associated with adequacy of methods and reporting. DESIGN: Retrospective analysis of RCTs included in Cochrane reviews. Time series describes the proportion of RCTs using adequate methods, inadequate methods and poor reporting. A multinomial logit model tests potential factors associated with methods and reporting, including funding source, first author affiliation, clinical trial registration status, study novelty, team characteristics, technology and geography. DATA: Risk of bias assessments for random sequence generation, allocation concealment, blinding of participants and personnel, blinding of outcome assessment, incomplete outcome data and selective reporting, for each RCT, were mapped to bibliometric and funding data. OUTCOMES: Risk of bias on six methodological dimensions and RCT-level overall assessment of adequate methods, inadequate methods or poor reporting. RESULTS: This study analysed 20 571 RCTs. 5.7% of RCTs used adequate methods (N=1173). 59.3% used inadequate methods (N=12 190) and 35.0% were poorly reported (N=7208). The proportion of poorly reported RCTs decreased from 42.5% in 1990 to 30.2% in 2015. The proportion of RCTs using adequate methods increased from 2.6% in 1990 to 10.3% in 2015. The proportion of RCTs using inadequate methods increased from 54.9% in 1990 to 59.5% in 2015. Industry funding, top pharmaceutical company affiliation, trial registration, larger authorship teams, international teams and drug trials were associated with a greater likelihood of using adequate methods. National Institutes of Health funding and university prestige were not. CONCLUSION: Even though reporting has improved since 1990, the proportion of RCTs using inadequate methods is high (59.3%) and increasing, potentially slowing progress and contributing to the reproducibility crisis. Stronger incentives for the use of adequate methods are needed.