CHANGES IN THE PREVALENCE OF COALWORKERS' PNEUMOCONIOSIS AMONG MINERS AND EX-MINERS IN THE RHONDDA FACH 1951-61 BY

The changes in the prevalence of pneumoconiosis among miners and ex-miners in the Rhondda Fach in three age groups at three different times (1951, 1953, and 1961) have been investigated. The radiographs were re-read with the dates concealed, in a randomized order, by one observer. Later a stratified sample was classified for technique. The results of the randomized readings, standardized for technique, suggest an increase in prevalence in the older age groups and a slight decrease in the youngest. Further analysis suggests that the changes are not due to differential migration and mortality, and it is concluded that they are probably due to the progression of simple pneumoconiosis. This is thought to be mainly due to dust exposure, but the possibility of progression occurring in the absence of dust exposure is not excluded. The work on which this paper is based was stimulated by seeing the figures for the change in prevalence of coalworkers ' pneumoconiosis among the underground population of a South Wales col-liery (Table 1) in 1951 and 1961. The two survey