Uses of Epidemiology
Epidemiology provides the facts about community health; it describes the nature and relative size of the problems to be dealt with, and 'maps' are produced of such scales as are required or possible. Results are sometimes surprising—at any rate in contrast with the type of problem of which there is general awareness and concern in the public health movement. Over 10% of sickness absence in male industrial workers in 1951 was ascribed to 'bronchitis' (16 million days). 'Psychological' disorders accounted for >13 million days; gastric and duodenal ailments for over 11 million, 'rheumatism and arthritis' for over 11 million.

Usually, however, we are concerned with the distribution of phenomena, and not merely their totals. Such distributions are firstly in terms of age and sex (race or colour, where applicable), economic status and so on. Table 1 is an example of a social-economic distribution in relation to primagravidae in Aberdeen. It shows some interesting similarities, as in nutrition, and the remarkable differences that still remain between the social classes in 'capital' goods like housing and education (in these early days of the Welfare State). There is a wide range of reproductive performance in this relatively homogeneous town. Such demonstration of inequalities between groups is a standard function of epidemiology, and it can be put to many uses—for example, in the same field as Table 1 to identify 'vulnerable groups' meriting special attention by health services (Figure 2 ).


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Three groups with particularly high foetal and infant mortality rates, England and Wales, 19498