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Evaluation of three retrospective exposure assessment methods.

OBJECTIVE
To evaluate three methods for assessing retrospective exposures of acrylonitrile workers.


METHODS
Three methods used to develop historical exposure estimates for a retrospective cohort mortality study of acrylonitrile workers were considered. The first method was deterministic, incorporating estimates of the impact of changes that took place in the workplace. The second method used the ratio of the mean of the measurements for three similar jobs to estimate a fourth similar job. The third method was based on the development of homogeneous exposure groups (HEG). Estimates of acrylonitrile exposure were developed using these three methods and compared with measurement means (observed means) across three categories of airborne exposure concentrations (<0.5, 0.5-0.99 and >or=1 p.p.m.) and three categories based on the number of measurements used to develop the estimate (<10, 10-29 and >or=30).


RESULTS
The correlation between the estimates and the observed values was about 0.65 for all three methods. Estimates using the deterministic method tended to overestimate the observed means by 17%, but the number of estimates was not above or below the observed means more often than expected. There was no statistically significant relationship between the exposure estimates and the acrylonitrile concentration in the air or the number of measurements used to develop the estimates. The estimates averaged within 60% of the observed means when concentrations were above 0.5 p.p.m. and 25% regardless of the number of measurements on which the estimates were based. Estimates from the ratio method were randomly distributed above and below the observed means and averaged 70% above the observed means. The air concentration did not affect the performance of the method, although above 1 p.p.m. the estimates were within 40% of the observed means. The number of measurements comprising the estimates was related on a relative scale to the performance of the method. Exposure estimates using the HEG method were neither greater nor less than the observed means more often than what was expected. The method did better as concentration and the number of measurements increased. The estimates were within 60% of the means at >0.5 p.p.m. and for all measurement categories. Overall, there was no statistically significant difference between the estimates derived from the three estimation methods.


CONCLUSIONS
All methods performed reasonably well, but the deterministic and HEG methods appeared to develop estimates closer to the observed means for concentrations >0.5 p.p.m., regardless of the number of measurements.