EMPIRICAL-EVALUATION OF THE INFLUENCE OF CONTROL SELECTION SCHEMES ONRELATIVE RISK-ESTIMATION - THE WELSH NICKEL WORKERS STUDY

Objective-To perform an empirical evaluation of the theory that relati ve incidence rate (RIR) and relative risk (RR) can be directly estimat ed from case-control studies that have different sampling schemes of c ontrols. Methods-With data from the South Wales nickel refinery worker s (SWNRW) study, a nested case-control study of the relation of nickel exposure to respiratory cancers, was conducted within each of four fi xed subcohorts that differed for stability of exposure, incidence rate s and RIR. Odds ratios (ORs) and confidence intervals (CIs) were estim ated either with all available controls or with randomly sampled subse ts of controls. Results-Respiratory cancers were not rare as risk of n asal and lung cancer in workers unexposed to nickel varied from 15% to 26% over the full risk period. The RIR was adequately estimated by th e OR when controls were identified concurrently to case occurrence thr oughout the risk period. The RR was well approximated with the OR when controls were a sample of the study base. Conclusions-These results a dd empirical support to the theory that the RIR or the RR can be valid ly estimated in case-control studies. Overall, this theory is relative ly tolerant of large departures from the stability assumptions of expo sure and of incidence.