Smoking and coalworkers' simple pneumoconiosis.

The attack rate of simple pneumoconiosis in 2723 British coal miners is considered in relation to the men's dust exposures and smoking habits. A complementary analysis is presented, using less precise radiological data, of prevalence and attack rates in an independent group of miners. One of the analyses suggests that, at high dust exposures, smoking may be associated with an increased risk of developing pneumoconiosis: but the most sensitive statistical test used reveals that the apparent effect might well be due to change factors (P not less than 0.09). The possibility is investigated that the net observed effect is the resultant of conflicting tendencies in sub-groups characterized by their responses to questions on phlegm production. There is no evidence to support this hypothesis. It is concluded that the main variable determining the development of simple pneumoconiosis is exposure to airborne dust, and that this effect is not modified appreciably by whether or not coal miners smoke.