of exposure relationships generally have not been identified. These investigators believe an overriding fault in the field is the assumption of differences among the elderly population and younger populations that have not been documented. Kasl and Berkman consider this belief to be an obstacle to a "dispassionate" examination of the evidence. Consequently, further work must be done to increase standardization of definitions and strengthen measurement.
The few existing studies of the prevalence of social isolation indicate that a total absence of relationships is relatively rare for the elderly.23 Furthermore, when social isolation is identified as a condition of older individuals, the phenomenon is generally accepted as the continuation of a lifelong pattern rather than a development of late life. However, elderly individuals, perceiving themselves to be frail and dependent, may isolate themselves to disguise their loss of autonomy. The limited empirical evidence available on the prevalence of social isolation1,46 seems to corroborate a low prevalence of true social isolation. Theoretical as well as empirical work on the effect of social isolation makes use of social support as an indicator of the degree of social isolation.
Although evidence of total isolation among older individuals may not exist, there has been work suggestive of the existence of relatively low levels of social support for some elderly. In a follow-up study of research involving a community population, 35 percent of the older individuals surveyed reported that they had no confidant (a confidant being defined as someone with whom to discuss serious problems, who was easily available, and with whom there was at least monthly contact).17
The very early, almost primitive level of definition, measurement, and hence attribution of specific risk to this factor in disease and its outcome is undoubtedly the basis for the lack of estimates of the cost of social isolation, although related areas have been studied. There have been rough estimates made of the cost to families and other care givers for specific diseases, notably Alzheimer's disease;16 in addition, there have been efforts made to analyze the cost-effectiveness of prevention programs for older individuals. The general