Fig. 3: The graph presents the use of the exposure data in two examples of study designs used in environmental epidemiology.
The top figure illustrates a risk set within a study on the incidence of lung cancer (ICD-10: C34) with a case (subject 2) and controls matched by age used in a Cox proportional hazard model to estimate long-term risks. The event (aquamarine star) and control (blue star) times are used to reconstruct backwards the exposure profiles in the three subjects, defined as 365-day (lag 0–364) averages of PM2.5 (light blue boxes). The bottom figure displays the same process to define risk sets for a time-stratified case-crossover to estimate short-term risks. The graph shows three separate subjects (unrelated to Table 1) with the event (aquamarine star) and controls (blue star) days matched on the day of the week in the same month, with exposure profiles defined as averages of lag 0–3.
