Table 1.
Comparison of the study sample with the representative sample
| Characteristica | Population sample (n = 2120) | Study sample (n = 1374) |
|---|---|---|
| Sex of the child (male), no (%) | 1080 (50.9%) | 647b (47.1%) |
| Lifetime methylphenidate use, no (%) | 288 (13.6%) | 238b (17.3%) |
| IQ of the child, mean (SD) | 6.20 (3.82) | 6.44b (3.88) |
| Family socioeconomic status, mean (SD) | 0.0 (1.0) | 0.68b (1.0) |
| Maternal age at birth of first child (years), mean (SD) | 25.8 (4.9) | 25.9 (5.0) |
| Mother high school diploma or higher, mean (SD) | 1778 (84.0%) | 1175b (85.5%) |
| Mother no high school diploma, no (%) | 339 (16.0%) | 198 (14.4%) |
| Intact family, no (%) | 1669 (78.7%) | 1099 (80.0%) |
| Non-intact family, no (%) | 443 (20.9%) | 272 (19.8%) |
| Hyperactivity–impulsivity (teacher rated, 8 years), mean (SD) | 2.24 (2.63) | 2.14 (2.61) |
| Inattention (teacher rated, 8 years), mean (SD) | 3.85 (3.32) | 3.72 (3.34) |
aBetween 1.9 and 11.6% missing data
bP < 0.01