Abstract
Using the data obtained by Cochrane from his prospective study of attack by progressive massive fibrosis in the populations of two mining valleys in Wales, logistic regression models have been established to investigate the complex structure of the data. The assessment of progressive massive fibrosis status made at the end of study of Cochrane was made without knowledge of the initial grade of simple pneumoconiosis. The modeling approach adopted here enables allowance to be made for the appreciable differences in the percentage attacked by progressive massive fibrosis which exist in the two valleys. The prognostic value of initial time-of-survey category of simple pneumoconiosis among those men free from progressive massive fibrosis at that time has been utilized rather than the average derived from the initial and end-of-study grades. These investigations have led to the identification of a previously unrecognized and important influence of tuberculosis infection that is both consistent and unlikely to be a chance finding either as a main effect or in combination with other terms (p < 0.04). In marked contrast to previous investigations of these data, a clear gradient of increasing probability of attack with increasing age has been noted, rising from 17.6 percent at 25 to 34 years to 33.3 percent for those aged at least 65 years. The important multiplicative effect of tuberculosis and age on attack by progressive massive fibrosis that has been observed is unlikely to be a chance finding (p < 0.04) and suggests that the presence of this infection at an early age may have greater influence on the likelihood of attack than its presence at a later age. Higher grades of simple pneumoconiosis are found to be strongly associated with increased probability of development of progressive massive fibrosis. With elevated tuberculosis infection rates being experienced in certain areas of the United States, as population movements increase in the present changing economic conditions, improved health management techniques are likely to increase in importance. The current findings may aid development of such techniques, which in turn may facilitate control of the development of progressive massive fibrosis.