J N Morris


Int J Epidemiol. 2007;36(6):1165-1172. 

In This Article

Completing the Clinical Picture

The most obvious example of this function is the contribution of the epidemiological method in determining the sex and age incidence of disease. The calculation of accurate age-specific rates showing, for instance, that cancer of the ovary, and possibly of the breast, reach peak frequency late in middle age is of course a help in understanding these conditions, as are the relations with parity. But it is possible to go further. Epidemiology, being by definition concerned with all ascertainable cases in a population, often produces different pictures of disease from those derived only from hospitals, for example. Thus, half or more of the deaths of men from coronary heart disease in middle age (56% here) seem to occur in the first few days of the first clinical attack of 'coronary thrombosis' (Figure 5 ). A quite incomplete picture of coronary heart disease must result if many of these cases are excluded. But often these deaths are 'sudden', known only to the general practitioner and the coroner's pathologist. Special efforts are therefore needed to discover them, and, dependent on the success of such efforts, so may any picture presented of prognosis in this disease, of survival, and of the results of new treatments be very considerably modified.

Deaths from coronary heart disease during middle age: relation to first clinical attack. Male medical practitioners 40–64 years, 1940–52. There were 136 deaths in 13 years.13,22

The same is probably true at the other end of the spectrum: to get an idea of how much there is of mild ischaemic heart disease, minor and maybe atypical, reliance cannot be placed on the cases that happen to turn up in a particular practice or out-patient department, but an inclusive and extensive study is needed. (This principle is made use of in 'screening' surveys to detect early sub-clinical disease. Thus detected, as in diabetes, progression may be halted, and the surveys are thus a measure of control or prevention.) In brief, studies of the natural history of disease will be more complete and correctly proportioned if based on all the cases satisfying specified diagnostic criteria occurring in a defined population. Pneumoconiosis, byssinosis, rheumatoid arthritis and nutritional disorders such as anaemia come to mind in this context.[23,24,25]


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