Table 1.
Sample statistics
| Cohort 2 | Cohort 3 | Cohort 4 | |
|---|---|---|---|
| Sample characteristics | |||
| Pairs total | 1,036 | 1,058 | 980 |
| MZ twin pairs (% male) | 420 (45.5%) | 498 (43.8%) | 523 (40.5%) |
| DZ twin pairs (% male) | 616 (49.8%) | 560 (41.8%) | 457 (43.3%) |
| Included pairs1 | 1,035 | 1,043 | 540 |
| Age twins (SD) | 10.99 (0.33) | 16.99 (0.35) | 23.04 (0.82) |
| Age mothers (SD) | 42.94 (4.99) | 47.68 (4.60) | 52.45 (4.97) |
| Age fothers (SD) | 46.54 (5.36) | 50.20 (5.20) | 55.33 (5.51) |
Notes. MZ = monozygotic, DZ = dizygotic, SD = standard deviation. The percentage of male twin pairs relates to the total number of MZ, and DZ twin pairs, respectively;
1
Families in which both twins were living with at least one parent; excluded cases did not differ significantly from included cases in terms of the distribution of the SES indicators and cognitive abilities.