This study uses data from the 1995 National Survey of Midlife Development in the United States (MIDUS) (Brim et al. 1996). MIDUS is a nationally representative survey designed to study the effects of midlife development on the self-reported physical health, psychological well-being, and social consciousness of adults aged 25 to 75. To examine the genetic influences on the social and psychological components in this study, the MIDUS team developed the twin screening project in order to oversample adult twin pairs. The MIDUS twin screening project was conducted by two research organizations, ICR/AUS consultants and Bruskin Associates, who contacted randomly selected households by telephone and asked if there were “any twins in your or your spouse’s immediate family where BOTH of the twins are still living?” During the pre-test period, 14.8 percent of the households said “yes” to this question, with 2.3 percent being members of a twin pair and 12.5 percent of respondents with a twin pair in their family. They were then asked if it would be okay for the Harvard Medical School to contact them and their twin
