096 RETHINKING ANALYSIS OF ENVIRONMENTAL AND OCCUPATIONAL VARIABLES: TOWARDS A MORE INFORMATIVE APPROACH FOR TOTAL EXPOSURE, EXPOSURE RATE AND DURATION

Exposure rate, exposure duration and total cumulative exposure are the focus of most cancer risk analyses. From this triad, investigators generally highlight exposure rate and duration, although interpretation of these covariates as “independent” factors can be problematic. In a simple multiplicative relative risk (RR) model, the exposure rate parameter represents the ln(RR) per unit exposure rate at a fixed duration. With duration fixed, interpretation of the RR by exposure rate is distorted by changing total exposures. For example, at 30 year duration of cigarette smoking, RRs at 20 and 30 cigarettes per day reflect not only the different exposure rates, but also different total exposures, that is, 30 and 45 pack-years, respectively. Thus, the exposure rate parameter and the duration parameter do not represent “independent” effects, but implicitly embed the effect of total exposure. Identification of an “exposure–response” relationship is fundamental in establishing causality. An alternative perspective would be to estimate the effect of “total exposure” and any differential consequence associated with the manner of its delivery, that …