Table 3.
Potential research questions related to various effects under effect decomposition
| Effect | Research question |
|---|---|
| TEa | Overall, to what extent does X cause Y? |
| PDE | In particular, to what extent does X cause Y via pathways other than through M? |
| TIE | In particular, to what extent does X cause Y via M (i.e. due to X affecting M and subsequently, M affecting Y) and the possible interaction between X and M in affecting Y? In other words, the effect of exposure that “ would be prevented if the exposure did not cause the mediator” (i.e. the portion of the effect for which mediation is “necessary”) [19,47]. |
| TDE | In particular, to what extent does X cause Y via pathways other than through M, allowing M to boost up or tune down such effect at the same time? |
| PIE | In particular, to what extent does X cause Y via M only (i.e. due to X affecting M and subsequently, M affecting Y), not accounting for the possible interaction between X and M? In other words, the effect that the exposure would have had if “its only action were to cause the mediator” (i.e. the portion of the effect for which mediation is “sufficient”) (i.e. the portion of [19,47]. |
| CDE | What would be the effect of X on Y, when fixing M at a specific value for everyone in the population? |
| CDEsto | What would be the effect of X on Y, when allowing M to attain certain controlled distribution (via intervention) in the population? |
| RIE | What would be the effect of X on Y that is due to interaction between X and M only? |
| MIE | What would be the effect of X on Y that is due to both interaction between X and M and the fact that X causes M? |
| PAI | What would be the effect of X on Y that is due to interaction between X and M, regardless whether X causes M? |
a
TE: total effect, PDE: pure direct effect, TIE: total indirect effect, TDE: total direct effect, PIE: pure indirect effect, CDE: controlled direct effect (standard), CDEsto: stochastic controlled direct effect, RIE: reference interaction effect (referred to as “INTref” by VanderWeele), MIE: mediated interaction effect (referred to as “INTmed” by VanderWeele), PAI: portion attributable to interaction.