"The cancer risk associated with exposure to environmental and occupational carcinogens such as asbestos, benzene, radiation, or lifestyle carcinogens such as cigarette smoking depends on the entire history of exposure to the carcinogen, including the age of exposure and the time-varying intensity of exposure. While the importance of temporal aspects of exposure and risk has been highlighted for some time, the vast majority of epidemiological studies of cohorts use cumulative exposure as the measure of exposure, even when detailed exposure data are available for each member of the cohort. One reason is that the detailed history of exposure is difficult to incorporate in the traditional statistical models used to analyze epidemiological data. In contrast, time-dependent parameters associated with time-varying concentrations of exposure can be easily accommodated in statistical analyses based on multistage models. ..."

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