Figure 1.

Directed acyclic graphs describing the data generating processes for theoretical occupational health cohort studies of exposure (A) on an outcome (Y). The subscripts under A represent the time point of the exposure, so A1 is exposure that occurs in the first year of follow-up, A2 represents exposure in the second year, and A0 represents exposure that occurs at time 0 prior to the start of follow-up. U represents an unmeasured covariate affecting either an adverse health status (H) or work status (W) and the outcome (Y). Solid arrows represent the relevant causal effect of exposure on the outcome unmediated by future exposure, while hollow arrows represent pathways that constitute the Healthy Worker Survivor Effect mechanisms. a) Displays the time-varying confounding on the causal pathway that occurs via adverse health status (H). b) Displays the selection process that occurs when researchers condition on work status (W) by choosing a population of active workers for follow-up.