Control charts for the standard mortality ratio.

The Registrar General for England and Wales tells us not only how fast our species is killed, but what kills it, and the preference a specified disease has for different age-groups and for different occupations. The selectivity in the action of the various killers of our species with regard to social status and occupation has found expression in the so-called Standard Mortality Ratio (S.M.R.) which is the index the Registrar General uses for the purpose of describing the selective action of diseases. The S.M.R. may be briefly explained thus. The Registrar General calculates " standard deaths," which are the numbers obtained by applying the general mortality rates of Table 3 of the Registrar General's Decennial Supplement England and Wales, Part IIA, Occupational Mortality, 1931, for all males, all married women, or all single women, as the case may be, at the appropriate age-groups, 20-25-35-4555-65, to three times the census population of the occupational group as given inTable 4 of the Report, and summing the products. They represent the deaths which would result in an occupation group if that group were exposed at each age to the standard mortality risks. The S.M.R. is the percentage ratio of the deaths actually registered for the group to the calculated standard deaths. There is, however, apart from systematic and accidental errors of diagnosis, a type of error to be taken into account in comparing S.M.R.s. This is the error due to the fact that the people following