Twins from the MATCH study were selected from female same-sex pairs from both cohorts. PACER twins were selected from male same- and opposite-sex pairs from Cohort II. Reassessment of twin parents and co-twins by telephone interview and self-report questionnaire began in 2000 and 2005 for MATCH and PACER studies, respectively. The present analyses are based on questionnaire data from 874 MATCH twins (from 337 MZ and 280 DZ pairs) reporting on 1643 offspring, and 411 PACER twins (from 116 MZ, 87 same-sex DZ, and 171 opposite-sex DZ pairs), of whom 367 provided reports on 756 offspring and 44 biological co-parents (mothers in the case of twin fathers) reported on 93 offspring. In all, questionnaire data were available from 1285 parents reporting on 2492 offspring. Combined samples sizes by risk group are shown in Table 2, with sample characteristics provided in Table 3. Average age of parents was 42.01 (SD = 4.08), ranging from 32 to 65 years. The average age of offspring was 14.14 years (SD = 3.77), with roughly equal proportion of male (51%) and female (49%) offspring.
