Does intact pair status matter in the study of African American twins? The Carolina African American Twin Study of Aging.

In twin research, typically both members of a pair must participate. Survivorship of members of intact pairs compared to surviving members of nonintact twin pairs may reflect differences in psychosocial and health factors, and represent a potential selection bias relative to the general population. The purpose of the present study is to examine health, cognition, and well-being among members of African American intact twin pairs compared to individuals from nonintact twin pairs. Data from the Carolina African American Twin Study of Aging (CAATSA) were used for analyses. Subjects ranged in age from 25 to 89 years of age (mean = 59.78 years, SD = 12.84 years). CAATSA implements a 3-h protocol to collect data on demographics, health, cognition, and well-being. Data from one randomly selected member of each twin pair (N = 78) was compared to data from surviving members of nonintact twin pairs (N = 52). The results indicated significant differences on 11 of the 39 measures (i.e., age, education, forced expiratory volume, mean standing and sitting systolic and diastolic blood pressures, cognitive impairment score, alpha span, digit symbol, and logical memory). In each case, members of intact twin pairs performed better than surviving members of nonintact twin pairs. After controlling demographic variables, only blood pressures differed between the groups. It appears that using only pairs in research on older African American twins may represent a selection bias in estimating origins of individual variability in cognitive functioning and health but not psychological well-being.