Health sciences students should understand the fundamentals of epidemiologic methods that can lead to major advances in the treatment of disease. To this end, the research process is defined and a three-dimensional model that considers some basic elements of epidemiologic research—time, place, and strategy—is described. The strategies available to the investigator (descriptive, analytic, and experimental) and the possible time frames (retrospective, concurrent, and prospective) are illustrated in terms of field investigations that involve problems of infection, nutrition, dysplasia, metabolism, and cancer. It is believed that epidemiologic studies, no matter where they are performed, have certain features in common, especially those related to the elements of strategy and time.
(JAMA 239:328-330, 1978)