Figure 1.

Causal diagrams reflecting the application of life-course theories (in the absence of time-varying confounding) to the example of depression in early, mid-, and late life and subsequent stroke risk (in the absence of time-varying confounding). A) The accumulation model, in which each exposure to depression has a direct effect on stroke; B) the early-life critical period model, in which only early-life depression affects stroke; C) the pathway model, in which early- and midlife depression influence stroke only via their impact on late-life depression. Note that all 3 panels show early-life depression being associated with late-life depression only through midlife depression; the plausibility of this assumption must be considered on a case-by-case basis.