MORTALITY IN COALWORKERS ' PNEUMOCONIOSIS RELATED TO LUNG FUNCTION: A PROSPECTIVE STUDY* BY

In 1949, 126 coalminers, chosen to cover the whole radiological range of coalworkers ' pneumo-coniosis, were subjected to a battery of physiological tests of lung function, clinical investigations, and anthropometry. During the ensuing 12 years 40 of these men died. An analysis of the original measurements was carried out in an attempt to identify the particular features of the disturbance of lung function associated with pneumoconiosis which were most related to the rate of dying. The men were grouped into seven classes-survivors, and those dying within the six two-year intervals of the 12-year follow-up period. The variation of the means of these classes, for each of the measurements made, then has six degrees of freedom, which implies that six uncorrelated measurements would suffice to describe it completely. Eighteen measurements were in fact available for each man, all of course highly intercorrelated and so in part providing redundant information. The method of analysis adopted was to find a linear combination of the 18 measurements which discriminated best between the seven classes, a second combination, uncorrelated with the first, which was the second best discriminator, and so on. Six such combinations, canonical variates, would then contain all the information provided by the variation of the seven classes, and the relative magnitude of the contribution made by each original test to each canonical variate woul