An empirical approach for deriving information on total duration of exposure from information on historical exposure

Exposure duration is an important component in determining long-term dose r ates associated with exposure to environmental contaminants. Surveys of exp osed populations collect information on individuals' past behaviors, includ ing the durations of a behavior up to the time of the survey. This paper pr esents an empirical approach for determining the distribution of total dura tions that is consistent with the distribution past durations obtained from surveys. This approach is appropriate where the rates of beginning and end ing a behavior are relatively constant over time. The approach allows the i ncorporation of information on the distribution of age in a population into the determination of the distribution of durations. The paper also explore s the impact of "longevity" bias on survey data. A case study of the applic ation of this approach to two angler populations is also provided. The resu lts of the case study have characteristics similar to the results reported by Israeli rind Nelson (Risk Anal. 12, 65-72 (1992)) from their analytical model of residential duration. Specifically, the average period of time for the total duration in the entire population is shorter than the average pe riod of time: reported for historical duration in the surveyed individuals.