Data for brain volumes and global white matter microstructure and results of the tests for main effects of group, group by age interactions and dimensional IQ effects.

Abbreviations: ADHD, Attention-Deficit/Hyperactivity Disorder; FA, Fractional Anisotropy.
Note: covariates for gender, age and slice thickness on T1 were included in all analyses (except the analysis of cerebral FA where there were no differences in slice thickness); a. nControl = 98, nADHD = 90; b. raw ventricular volumes are tabulated. For analyses, these measures were log-transformed due to a deviation from normality; c. nControl = 96, nADHD = 90; d. nControl = 34, nADHD = 30, not split in IQ groups due to small group size; e. This column reports analyses of age effects on the whole diagnostic groups (not split by IQ). Analyses on the group with age<14 years (ncontrol = 93, nADHD = 85) showed the same pattern of results except for Mean Cortical Thickness (p = .028). Both groups showed decreasing thickness with age, but the regression line was steeper in the control group; f. This column reports analyses of IQ effects where IQ is treated as a dimensional measure, with its effects tested on the whole diagnostic groups. As these analyses were performed on continuous measures, three above median IQ outliers were excluded from structural MRI dataset for the IQ analyses (see Methods).