The clinical trial as a paradigm for epidemiologic research.

The extent to which the clinical trial serves, and fails, as a paradigm for epidemiologic research in general is examined. It is argued, first, that the traditional paradigms--investigating epidemic and endemic occurrence of illness in the context of public-health activities, inclusive of the deployment of census, vital and morbidity statistics and sample surveys--are misleading for scientific research. Major examples of the consequences of these paradigms are the preoccupations with time and place, and with "the general population" or some other "target population"--both alien from the vantage of clinical trials and, indeed, of science in general. Then it is shown, by the use of the clinical trial paradigm, that traditional epidemiologic thought and practice in cause-effect research are misguided in the context of such common contexts as the use of empirical contrasts between exposure and unspecified nonexposure, the employment of "representative" distributions of determinants, and, even, as to the belief that cohort and "case-control" studies constitute alternatives to each other. On the other hand, it is argued that for etiologic research the ordinary (parallel) clinical trial is misleading as a paradigm, especially as for learning about the essential temporal aspects of the cause-effect relation.