The study consisted of 909 twin pairs and their spouses from both the first and second cohort of the Twin and Offspring Study in Sweden (TOSS), a two-cohort study of twin parents, one adolescent child and the spouse/partner. A more detailed description of the sample is available in a previous paper by Neiderhiser and colleagues (50). The same-sex twins included in the study were required to have a relationship of at least 5 years with their partner; while 82% were married, 18% were cohabiting but unmarried. This study used three different measures of pair-bonding behavior in the TOSS sample; the Partner Bonding Scale (PBS) (49), a martial crisis item from a life event questionnaire based on the Social Readjustment Rating Scale (51) and spouse reports of marital quality using the Dyadic Adjustment Scale (DAS) (52). DNA samples were collected for all twins participating in TOSS and all family members who participated as part of cohort 2. Since the first TOSS cohort only includes twin mothers, DNA is available for a larger amount of adult women than men. DNA was extracted
