The supposed superiority of randomized over non-randomized studies is used to justify claims about therapeutic effectiveness of medical interventions and also inclusion criteria for many systematic reviews. However, the view that randomized trials provide better evidence has been
challenged by philosophers of science. In addition, empirical evidence for average differences between randomized trials and observational studies (which we would expect if one method were superior) have proven difficult to find. In this paper we review the controversy surrounding the relative merits of randomized trials and observational studies.
Core reading: Howick and Mebius [forthcoming]