A TASK-BASED STATISTICAL-MODEL OF A WORKERS EXPOSURE DISTRIBUTION .2.APPLICATION TO SAMPLING STRATEGY

A task-based statistical model of a workers exposure distribution for an airborne chemical toxicant is applied to estimating the long-term a verage exposure level, mu. The precision in estimation is represented by the variance of the sample estimator, denoted by Var[mu]. A traditi onal sampling strategy consists of integratively measuring the 8-hr ti me-weighted average exposure level on randomly selected workdays, and computing the sample mean; this strategy is termed ''simple one-stage cluster sampling; where each 8-hr workday is a cluster of thirty-two 1 5-min periods. Three alternative strategies involving measurements of 15-min TWAs are examined: simple random sampling of 15-min periods, an d stratified random sampling of 15-min periods with proportional alloc ation by task, and with optimum allocation by task. All four survey de signs provide unbiased estimates of mu. However, for a fixed cost, the stratified sampling designs may provide a lower Var[mu] than simple o ne-stage cluster-sampling for less work time monitored.