Examination of Potential Sources of Bias in the US Coal Workers' Health Surveillance Program

Objectives. We examined the potential influences of certain selection factors on the utility of the Coal Workers' Health Surveillance Program (CWHSP) data for tracking disease distribution and trends. Methods. We combined data from the CWHSP and the Energy Information Administration to examine any influence of variable worker participation on observed disease prevalence. We evaluated effects of differential participation by coal mining region, temporal changes in employment, and active surveillance efforts. Results. The published findings of pneumoconiosis distribution and trends from the CWHSP were robust compared with the various participation factors that might have affected their validity for population-based estimates of disease burden. Exploration of factors that could potentially bias the findings generally led to small increases in the primary estimates, mostly for the early years of the program. Conclusions. We confirmed previously reported findings that there was a high prevalence of coal worker pneumoconiosis (CWP) around 1970-1974, a substantial decline in 1995-1999, and indications of an increase since then. Overall our findings suggest that the previously reported distribution and trends in CWP prevalence were broadly accurate.