The study analysed the mortality rates (obtained from death certificates and census returns contained in the Decennial Supplement on Occupation and Mortality) in England and Wales during 1970-1972, by occupation and social class. Mortality rates were calculated in terms of the standardized mortality ratio (SMR):

(SMR =observed deaths X 100)
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                expected deaths

A major finding of the study was that mortality was inversely related to social class. This result may be explained in two ways. Either the incidence of TB was greater in the lower classes or, there was a significant difference in case fatality between the classes. Based on the available information, it was concluded that there were good reasons to suppose that both explanations were important.