Choosing between randomised and non-randomised studies: a systematic review

Rating: Randomised controlled trials are often held up as the “gold standard” of medical research, and it is commonly believed that the size of a treatment effect is exaggerated in non-randomised studies. In these days of evidence based medicine, however, where is the empirical evidence that this is so? A widespread criticism of randomised controlled trials is that they are based on highly selected individuals. Are there systematic differences between patients included and excluded in such trials, and do these influence the measured treatment effect? These are just a few …