Table 1.
Demographic characteristics of the sample
| MZ | DZ | Siblings of twins | Singletons | Total | |
|---|---|---|---|---|---|
| Sample size | 252 | 133 | 110 | 318 | 813 |
| Mean age at first scan (years ) | 11.3 (3.8) | 9.6 (3.5) | 12.0 (4.4) | 11.7 (5.1) | 11.3 (4.4) |
| Mean scan interval (years ) | 2.4 (0.66) | 2.4 (0.67) | 2.3 (0.86) | 2.3 (0.85) | 2.4 (1.1) |
| Gender | 117 F (46%) | 62 F (47%) | 61 F (55%) | 143 F (45%) | 383 F (47%) |
| 135 M (54%) | 71 M (53%) | 49 M (45%) | 175 M (55%) | 430 M (53%) | |
| SES (Hollingshead index) | 44.2 (18.6) | 43.0 (15.1) | 43.0 (17.9) | 40.5 (20.4) | 42.6 (18.7) |
| Handedness | 218 R (87%) | 108 R (81%) | 88 R (82%) | 284 R (89%) | 698 R (87%) |
| 16 M (6%) | 15 M (11%) | 7 M (7%) | 18 M (6%) | 56 M (7%) | |
| 14 L (5%) | 10 L (8%) | 12 L (11%) | 14 L (5%) | 50 L (6%) | |
| FSIQ | 110.3 (12.1) | 110.7 (11.5) | 113.4 (13.4) | 115.4 (12.9) | 112.7 (12.7) |