Randomized trials are not black boxes

Abstract

Randomized trials of medical interventions are frequently treated as a “black box” (Howick et al. 2013). On this view, randomized trials provide a way to assess an intervention (input) in terms of the outcomes it generates (output) without being concerned about the details of the mechanism(s) by which the intervention produces the outcomes. The ability of randomized trials to assess the efficacy of an intervention in the absence of a complete understanding of the mechanisms at play has been identified as a key argument in their favour (Cartwright 2010, p. 64). However, there is still a lot of reliable evidence of mechanisms—especially in contexts such as clinical drug development. Given the importance of this evidence to the design, interpretation and application of randomized trials, I argue that characterising randomized trials as a black box is inaccurate and unhelpful.