Parental separation prior to twins’ age 18 was coded from parent and Waves 1, 3, 4 and 5 twin interviews. Consistent with previous work (Waldron et al., 2013), parental separation was defined as change in marital and/or cohabitation status of biological parents for reasons of relationship dissolution. Twins’ age at parental separation was coded from year parents’ marriage ended or, if missing, age last lived with both parents. Age at separation in families where separation occurred prior to twins’ birth was coded as a fraction of a year.
