Estimation of cumulative exposures for the national study of coal workers' pneumoconiosis

Estimates of cumulative exposure to respirable coal mine dust were derived for a subcohort of Round Four of the National Study of Coal Workers’ Pneumoconiosis on the basis of Mine Safety and Health Administration (MSHA) sampling data. The subcohort includes Round Four participants who began mining work in 1970 or later. Using a sample of the MSHA exposure data, a procedure was developed for estimating mean exposures by three-way occupation/mine/year-specific strata. Occupation was defined by a standard MSHA coding scheme for coal mining operations. Where data for a particular three-way stratum were lacking, mean values of the appropriate two-way or one-way strata were substituted in the following order: 1) occupation/year, 2) mine/year (within broad occupational groups), and 3) year (within broad occupational groups). Since some three-way occupation/mine/year estimates had large variances, the threeway means were combined with two-way occupation/year means to minimize the mean squared error. Cumulative dust exposure, in milligrams per cubic meter-years (mg/m3-years), was then calculated for each cohort member. Cumulative exposure was compared with years worked and years worked underground, parameters which have been used as surrogates for cumulative exposure in past studies of respiratory health in United States miners. Under the assumption that cumulative exposure, which incorporates quantitative exposure concentrations, estimates a parameter closer to the actual dose received, cumulative exposure will provide a significant improvement in the accuracy of any modeled exposure-response relationship.