Gathering Evidence of Mechanisms

Abstract

In this chapter we put forward more theoretical proposals for gathering evidence of mechanisms. Specifically, the chapter covers the identification of a number of mechanism hypotheses, formulation of review questions for search, and then how to refine and present the resulting evidence. Key issues include increased precision concerning the nature of the hypothesis being examined, attention to differences between the study population (or populations) and the target population of the evidence assessors, and being alert for masking mechanisms, which are other mechanisms which may mask the action of the mechanism being assessed. An outline example concerning probiotics and dental caries is given. (Databases that may be helpful for some searches can be found online in Appendix A).In the next three chapters, we develop core principles for evaluating efficacy and external validity. In this chapter we put forward proposals for gathering evidence of mechanisms. Then, in Chap. 6 we discuss how to evaluate this evidence. In Chap. 7, we explain how this evaluation can be combined with an evaluation of correlation in order to produce an overall evaluation of a causal claim.In the case of efficacy, where clinical studies find a correlation between the putative cause and effect, the task is to determine whether this correlation is causal by looking for further evidence of mechanisms. In order to evaluate efficacy, it is necessary to determine the status of the general mechanistic claim, i.e., to ask whether the correlated putative cause and effect are also linked by a mechanism that can account for the extent of the observed correlation.In the case of external validity, the existing evidence may establish causality in a study population that differs from the target population of interest. Here the relevant general mechanistic claim that needs to be evaluated is that mechanisms in the study and target population are sufficiently similar.

Rigour versus the need for evidential diversity

“…For this purpose the pToc approach provides a nice supplement to Chapter 5 ofParkkinen et al (2018) ('Gathering Evidence of Mechanisms') which outlines steps for gathering evidence but does not detail what diverse kinds of evidence should be gathered.…”