ABSTRACT
The development of intelligence testing and the early studies of suicide had established the value of the ecologist's method; and the older psychiatrists, as Lewis has pointed out, were familiar with such basic epidemiological themes as the relationship between mental disorder and migration, isolation, occupation, and socio-economic change. The epidemiologist must identify his cases before he can count them, and he should be able to define and classify what he identifies. The nature of most psychiatric disorders, however, is so ill-defined as to preclude an aetiological classification. Within the major functional psychoses diagnostic practices have been shown to differ widely. In the use of epidemiological techniques as aids to the completion, or extension, of the clinical picture of mental disease, perhaps the most interesting development in this country has been the new look taken at the general practitioner under the National Health Service.
