The reporting of methods for reducing and detecting bias: an example from the WHO Misoprostol Third Stage of Labour equivalence randomised controlled trial

We describe an innovative and practical design for the boxes for packing the drugs as a way of increasing the security of allocation concealment and blinding. We also assess ascertainment bias using sensitivity analyses, as some unblinding could have occurred due to a potential side effect of one of the drugs.The sensitivity analyses indicated that the conclusions about the relative effects of the treatments could be maintained even in the unlikely worst-case scenarios.Detailed description of the procedures protecting against common biases and of the assessment of ascertainment bias in this trial should allow readers to confidently appraise and interpret the results obtained. In addition, our experiences will assist others in planning trials in the future.In the attempt to reduce the risk of bias in clinical trials, the method used to assign treatments to trial participants is crucial for reducing selection bias. Randomisation is the method of choice, and also permits the use of probability theory to express the likelihood that any difference in outcome between treatment groups merely reflects chance. Successful randomisation in practice depends both on adequately generating an unpredictable allocation sequence, and also on concealing that sequence until assignment occurs [1,2]. Blinding the identity of treatments to the investigators, participants, and evaluators (sometimes using placebo) also reduces the risk of bias after assignment of treatments. Knowledge of treatment allocation could lead to selective withdrawals before the treatment starts, selective loss to follow-up (both selection biases) and/or to a subjective assessment of the outcome (ascertainment bias).Inadequate methodological reporting of randomised clinical trials (RCTs) is associated with bias in the estimation of treatment effects [3]. Incomplete or inaccurate reporting impairs the critical appraisal of the quality of clinical trials, which is important to assess the validity of the results of th