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Characteristics of the sample
| Characteristics | Case | Control |
| Children, n | 296 | 335 |
| Age, yr (mean ± SD) | 11.89 ± 2.62 | 11.84 ± 2.49 |
| Male sex, % | 48.6 | 49 |
| Ethnicity, % | ||
| Caucasian | 77.5 | 82.6 |
| African American | 5.8 | 5.7 |
| Asian | 6.1 | 8.7 |
| Hispanic | 4.8 | 2.4 |
| Native American | 0.7 | 0.3 |
