Healthy worker effect in a longitudinal study of one-second forced expiratory volume (FEV(1)) and chronic exposure to granite dust

Background, Low level effects of granite dust on one-second forced expiratory volume (FEV,) are estimated in 618 Vermont granite workers followed for 5 years with annual pulmonary function tests. Reduced pulmonary function has already been reported for the subset of subjects lost to follow-up (dropouts) suggesting possible bias in analyses based only on survivors, Method. Healthy worker selection bias is directly assessed by comparing the dose-response associations between survivors who remained in the study for the full 5-year observation period and the dropouts. Results. The 353 survivors had an FEV, of 96% of predicted at baseline and were losing FEV, at an average rate of 44 ml/yr. No association was found in this group between the rate of FEV, decline and lifetime dust exposure. However, the 265 workers with incomplete follow-up, 'dropouts', had a lower FEV, at baseline (94%) and were losing FEV, at an average rate of 69 ml/yr. The dose-response parameter in this group was estimated to be 4 ml/yr loss per mg/m(3)-year and was statistically significant. Conclusions. These results provide an illustration of bias due to the healthy worker effect and an example of the failure to detect a true work-related health effect in a study based only on a 'survivor' population.