Identification of operating mediation and mechanism in the sufficient-component cause framework.

The assessment of mediation and mechanism is one way to more deeply explore cause-effect relationships, providing a stronger test and explanation of the observed associations. Most previous studies have described direct and indirect effects in terms of potential outcomes and response types, exploring mediation analysis in the counterfactual (= potential-outcome) framework. A recent paper by Hafeman (Eur J Epidemiol 23(11):711-721, 2008) provided a conceptual description of mediation in the sufficient-component cause framework, and VanderWeele (Eur J Epidemiol 24(5):217-224, 2009) explored the distinctions and relationships between the concepts of mediation and mechanism. This study builds on this prior work and demonstrates that further insight can be given by elucidating the concepts of mediation and mechanism in the sufficient-component cause framework, distinguishing their operation from presence. The careful consideration of the concepts of mediation and mechanism can clarify the relationship between them. Then, the present article describes how investigators can identify mediation as well as mechanism by showing their correspondence with direct and indirect effects in the counterfactual framework. This study also demonstrates how a researcher can decompose the total effect into the effect due to mediated paths and the effect due to non-mediated paths in terms of the probabilities of background factors of sufficient causes.