Assessing Risk of Bias in Randomised Clinical Trials Included in Cochrane Reviews: The why is Easy, the how is a Challenge

Randomised clinical trials are o en inadequately reported and may be inadequately conducted.Any associated biases could impact seriously on the findings and conclusion of a systematic review.Authors of systematic reviews thus need to assess the risk of bias in included randomised clinical trials.In this 20th Anniversary editorial, we look at the evolution of guidance on appraising studies included in Cochrane Reviews.Assessing the methodological 'quality' of included trials was addressed from the earliest days of The Cochrane Collaboration, although the phrase 'risk of bias' came into use later.In 1994 one of the first editions of the Cochrane Collaboration Handbook recommended that reviewers should routinely assess the adequacy of allocation concealment, and that they could consider assessing blinding and attrition, based on a seminal empirical study by Schulz and colleagues.[1]Over the next decade several Cochrane Review Groups developed di erent recommendations for assessing risk of bias.Of 50 Cochrane Review Groups surveyed in 2007, 41 recommended using specific trial characteristics to assess risk of bias and nine either recommended using a quality scale or made this optional.Most groups suggested assessing the randomisation procedure (including concealment of allocation), blinding, and attrition.[2] Assessing risk of bias in randomised clinical trials included in Cochrane Reviews: the why is easy, the how is a challenge (Editorial) 1