prevention seeks to decrease the number of new cases of a disorder or illness (incidence). Secondary prevention seeks to lower the rate of established cases of the disorder or illness in the population (prevalence). Tertiary prevention seeks to decrease the amount of disability associated with an existing disorder or illness. Although the goals of these three types of prevention appear to be clear-cut, in practice there is considerable disagreement about their usage.

The classic example of primary prevention within a public health context was the history-making action in the nineteenth century of John Snow (Last, 1988), who removed the handle of the Broad Street water pump in London to halt the epidemic of cholera in the neighborhood. Despite very little understanding of cause and effect, the prevention effort was successful. Gradually, the knowledge base regarding infectious diseases expanded.

In the original classification system of primary, secondary, and tertiary prevention, there was an implied understanding of mechanisms linking the cause of the disease with the occurrence of the disease. Since the time this system was developed, research has advanced our understanding of the complexity of the association between risk factors and health outcomes. There is an increased appreciation for the importance of the interplay among the biological, psychological, and social, or biopsychosocial, factors in the expression of a physical illness. For the most part, knowledge of the intervening mechanisms is just beginning to be understood.

Recognition of this complex interaction regarding risk and protective factors and illness outcomes, and the lack of understanding about how risk factors lead to or are associated with the onset of illness, sometimes lead to a pessimistic view that prevention efforts are futile until etiology is better understood. Gordon (1987), however, was convinced that practically oriented disease prevention and health promotion programs could be based solely on empirical relationships, and this led him to propose an alternative classification system for physical disease prevention (Gordon, 1987, 1983). The system was based on a risk-benefit point of view; that is, the risk to an individual of getting a disease must be weighed against the cost, risk, and discomfort of the preventive intervention. Gordon's system consisted of three categories: universal, selective, and indicated. All three categories were meant to apply only “to persons not motivated by current suffering” (Gordon, 1983, p. 108). The three categories represented the population groups to whom the interventions were directed and for whom they were thought to be most optimal.

A universal preventive measure is a measure that is desirable for everybody in the eligible population. In this category fall all those



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