focus of this research. This eliminated 435 individual respondents who were not married. We then eliminated 254 individuals for whom co-twin data was not available because of discordant marital status. This resulted in a final sample of 379 twin pairs: 99 monozygotic (MZ) male pairs, 102 MZ female pairs, 82 dizygotic (DZ) male pairs, and 96 DZ female pairs. The mean age of the sample was 45.8 (SD=12.03, range 25–74). Participants had been married an average of 23 years (SD=13, range=0–56).
