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Stephen Senn
Consultant Statistician
Edinburgh
The intellectual illness of clinical drug evaluation that I have discussed here can be cured, and it will be cured when we restore intellectual primacy to the questions we ask, not the methods by which we answer them. Lewis Sheiner1
Cause for concern
In their recent essay Causal Evidence and Dispositions in Medicine and Public Health2, Elena Rocca and Rani Lill Anjum challenge, ‘the epistemic primacy of randomised controlled trials (RCTs) for establishing causality in medicine and public health’. That an otherwise stimulating essay by two philosophers, experts on causality, which makes many excellent points on the nature of evidence, repeats a common misunderstanding about randomised clinical trials, is grounds enough for me to address this topic again. Before, however, explaining why I disagree with Rocca and Anjum on RCTs, I want to make clear that I agree with much of what they say. I loathe these pyramids of evidence, beloved by some members of the evidence-based movement, which have RCTs at the apex or possibly occupying a second place just underneath meta-analyses of RCTs. In fact, although I am a great fan of RCTs and (usually) of intention to treat analysis, I am convinced that RCTs alone are not enough. My thinking on this was profoundly affected by Lewis Sheiner’s essay of nearly thirty years ago (from which the quote at the beginning of this blog is taken). Lewis was interested in many aspects of investigating the effects of drugs and would, I am sure, have approved of Rocca and Anjum’s insistence that there are many layers of understanding how and why things work, and that means of investigating them may have to range from basic laboratory experiments to patient narratives via RCTs. Rocca and Anjum’s essay provides a good discussion of the various ‘causal tasks’ that need to be addressed and backs this up with some excellent examples. Continue reading
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