Uses of Epidemiology
We may summarize what has been said in terms of some of the relations between epidemiology, the epidemiological method and clinical medicine.

Epidemiology studies populations, and all cases that can be defined in them. It is concerned not only with those whose troubles immediately present to particular clinical attention but with the sub-clinical, the undiagnosed, the cases treated elsewhere. It thus helps to complete the clinical picture and nature history of disease.

Epidemiology supplements the clinical picture: by asking questions that cannot be asked in clinical study—about the health of the community and of sections of it, present and past; by setting clinical problems in community perspective, describing their behaviour as group, not individual, phenomena, indicating their dimensions and distributions, and how much, and where, action is needed; by revealing problems and indicating where among the population these might best be studied.

Finally, epidemiology by identifying harmful ways of living, and by pointing the road to healthier ways, helps to abolish the clinical picture. This is its chief function and the one in greatest need of development today.