Abstract
Retrospective exposure assessment in epidemiologic studies is dependent on the availability of historical monitoring results, yet rarely are there sufficient results to rely upon them exclusively. An approach is described that has a formal structure for developing exposure estimates for an epidemiologic study using a variety of methods depending on the information available. The approach identifies criteria for determining what data are needed for each method and the hierarchy for using the methods. The estimation methods include: (1) calculating a mean from the monitoring results of a job; (2) identifying homogeneously exposed jobs and using the mean of the measurements for the jobs as the estimate; (3) applying a ratio of the measurement means of two jobs in one operation to a third job in another operation to estimate a fourth; (4) weighting by time various areas or personal (short or full-shift) measurements representing tasks or locations; (5) taking a deterministic approach that modifies a more recent exposure by estimates of exposure modifiers to reflect how changes in the workplace affected exposures; and (6) using professional judgment. The homogeneous exposure group, ratio, time-weighted, and deterministic approaches were evaluated for bias, precision, accuracy, and correlation. First, a subset of the monitoring results was removed from the entire data set for use as referent values. Estimates were developed using the four methods without the removed data and compared with the referent value. On average, the estimates tended to overestimate the measurements in the ratio method (bias = 77%) and underestimate them in the time-weighted method (-24%). The average difference between the means and the estimates using the homogeneous exposure group method and the deterministic method was zero. The imprecision was threefold to fourfold for the ratio and deterministic methods and 1.5 fold for the time-weighted and homogeneous exposure group methods. Correlations between the estimates and the measurement means ranged between 0.60 and 0.75 and were statistically significant. When the methods were evaluated using only the same cells, the homogeneous exposure group method performed best, followed by the deterministic method and then the ratio method. The time-weighted average method could not be evaluated because of the lack of measurement data for these cells.
