"A society's health status is not simply the sum of the health of individuals, but an emergent property. While epidemiology has evolved from the study of simple epidemics to the study of the determinants of population health, it is still appropriate to consider the population as the epidemiologist's patient. At the same time, the population is also our study subject - we study populations to identify ways to prevent disease in populations. This article illustrates some of the implications for the prevention of disease that result from treating society as our patient."

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