, Volume 33, Issue 2, pp 339-360

First online:

Mechanisms and the Evidence Hierarchy

  • Brendan ClarkeAffiliated withScience and Technology Studies, University College London
  • , Donald GilliesAffiliated withScience and Technology Studies, University College London
  • , Phyllis IllariAffiliated withScience and Technology Studies, University College London Email author 
  • , Federica RussoAffiliated withDipartimento di Studi Umanistici, Università degli Studi di Ferrara
  • , Jon WilliamsonAffiliated withPhilosophy, SECL, University of Kent

Rent the article at a discount

Rent now

* Final gross prices may vary according to local VAT.

Get Access


Evidence-based medicine (EBM) makes use of explicit procedures for grading evidence for causal claims. Normally, these procedures categorise evidence of correlation produced by statistical trials as better evidence for a causal claim than evidence of mechanisms produced by other methods. We argue, in contrast, that evidence of mechanisms needs to be viewed as complementary to, rather than inferior to, evidence of correlation. In this paper we first set out the case for treating evidence of mechanisms alongside evidence of correlation in explicit protocols for evaluating evidence. Next we provide case studies which exemplify the ways in which evidence of mechanisms complements evidence of correlation in practice. Finally, we put forward some general considerations as to how the two sorts of evidence can be more closely integrated by EBM.


Mechanism Difference-making Evidence Evidence of mechanism Evidence in medicine Evidence-based medicine