Latency analysis in epidemiologic studies of occupational exposures: Application to the Colorado Plateau uranium miners cohort

Background Latency effects are an important factor in assessing the public health implications of an occupational or environmental exposure. Usually, however latency results as described in the literature are insufficient to answer public health related questions. Alternative approaches to the analy sis of latency effects are warranted. Methods A general statistical framework for, modeling latency effects is de scribed. We then propose bilinear and exponential decay latency models far analyzing latency effects as they have parameters that address questions of public health interest. Methods are described for fitting these models to cohort or case-control data; statistical inference is based on standard lik elihood methods. Application A latency analysis of radon exposure and lung cancer in the Col orado Plateau uranium miners cohort was performed. We first analyzed the en tire cohort and found that the relative risk associated with exposure incre ases for about 8.5 years and thereafter decreases until it reaches backgrou nd levels after about 34 years. The hypothesis that the relative risk remai ns at its peak level is strongly rejected (P < 0.001). Next, we investigate d the variation in the latency effects over subsets of the cohort based on attained age, level and rate of exposure, and smoking. Age was the only fac tor far which effect modification was demonstrated (P = 0.014). We found th at the decline in effect is much steeper at older ages (60+ years) than you nger: Conclusion The proposed methods can provide much more information about the exposure-disease latency effects than those generally used. (C) 1999 Wiley -Liss, Inc.