SELECTION BIAS IN SAMPLES OF OLDER TWINS - A COMPARISON BETWEEN OCTOGENARIAN TWINS AND SINGLETONS IN SWEDEN

Twin studies are a powerful approach for estimating genetic and enviro nmental influences in later life, but the usual requirement that both twins are alive may introduce a selection bias in gerontological studi es relative to representative samples of nontwins. In the present stud y, samples of older twins and nontwins in Sweden were compared across the domains of vitality, well-being, physical and cognitive functionin g, and health utilization to evaluate possible selection bias. One mem ber of each twin dyad in the OCTO-Twin Study of intact twin pairs olde r than age 80 was randomly selected (N = 128) and compared with a popu lation-based sample of nontwins (N = 324) from the OCTO Study. Multipl e regressions adjusting for differences in demographic variables showe d significant effects for twin status in only 3 of 20 comparisons. The results suggest that twin pairs surviving into very late life are sim ilar to a representative sample of nontwins of the same age in health status and biobehavioral functioning. These findings support the gener alizability of twin studies for understanding genetic and environmenta l influences on aging, health, and behavior.