NIA, (2) describe selected, potential applications of these surveys for genetic study, (3) address the various modes of specimen collection applicable in population surveys, and (4) suggest a research agenda to realize these potential methodologic enhancements.
Many population surveys are conducted in the United States and elsewhere; there is no clear way to identify all of them. Many of the NIA-sponsored surveys are extensive in scope and themes, and several are conducted outside of the United States. Information on a selection of these surveys, the basic characteristics of which are described in Table 12-1 , was taken from the NIA document ''Databases on Aging," a summary of surveys relevant to the demography, economics, and epidemiology of aging, published in February, 1996.1 The surveys noted in Table 12-1 are not an exhaustive list of those available, nor does the table cite many of the survey data sets available in archive form for analysis. In some instances, the tabular information is simplified because of the complex, multiple sampling frames and the varied target populations and different survey intervals. On occasion, survey design and operational information were incomplete.
In summary, the survey study designs reveal the following: (1) the surveys vary dramatically in health-related content; many were intended largely to study behavioral, social, and economic issues; (2) most of the surveys are recent but inactive, and it is unclear whether participants could be located or recontacted to obtain additional information; (3) many of the surveys contain information on at least some family members, but sometimes this is limited to spouse pairs and the extent of documenting either nuclear or extended pedigrees is often limited or uncertain; (4) collection of bodily specimens—either blood or other tissues or fluids—is rare. In the few instances where specimens were collected, this was limited mostly to U.S. national samples and subsamples conducted by the U.S. National Center for Health Statistics; (5) follow-up rates for the longitudinal panels were generally quite good, including mortality follow-up when part of the protocol; and (6) the original investigators would almost always need to be contacted to explore further participant contact and any possibility of specimen collection, including the determination of ethical and administrative procedures. In general, this suggests that retrospective use of these surveys, particularly the inactive ones, would require additional resources and energy to suit them for genetic study, but nonetheless, a reasonable potential remains for exploitation of, at least, ongoing or planned surveys.