Table 1.
Participant Characteristics
| Characteristic | Group | Sex Difference | ||
|---|---|---|---|---|
| All | Male | Female | ||
| Number of Individuals | 108 | 67 | 41 | n.s. |
| Singleton | 63 | 35 | 28 | |
| Member of twin pair | 45 | 32 | 13 | |
| Handedness, No. | n.s. | |||
| Right | 99 | 62 | 37 | |
| Mixed | 4 | 3 | 1 | |
| Left | 5 | 2 | 3 | |
| Race, No. | n.s. | |||
| Caucasian | 98 | 62 | 36 | |
| African-American | 3 | 1 | 2 | |
| Asian | 2 | 1 | 1 | |
| Hispanic | 3 | 2 | 1 | |
| Other | 2 | 1 | 1 | |
| IQ | n.s. | |||
| Mean (SD) | 115 (11.8) | 116 (11.5) | 114 (12.4) | |
| SES | n.s. | |||
| Mean (SD) | 40 (17.6) | 39 (18.5) | 41 (16.2) | |
| Number of scans, No. | n.s. | |||
| 3 scans | 67 | 39 | 28 | |
| 4 scans | 31 | 22 | 9 | |
| 5 scans | 9 | 5 | 4 | |
| 6 scans | 1 | 1 | 0 | |
| Total | 376 | 236 | 140 | |
| Age Distribution of Scans (years) | ||||
| Mean (SD) | 15.2 (3.5) | 15.3 (3.5) | 14.9 (3.5) | |
| Range | 9.1–22.8 | 9.2–22.7 | 9.1–22.8 | |
n.s., not statistically significant at p < 0.05; SES, socioeconomic status.