Although subjects with and without ADHD had similar sociodemographic characteristics, ADHD subjects were somewhat older than controls (p<0.01) (). Thus, subsequent analyses are corrected for age.
CLINICAL AND DEMOGRAPHIC CHARACTERISTICS OF SAMPLE
In multivariate analyses including both diagnoses and age, DAT binding was statistically significantly different between diagnostic groups only in the right caudate (t=2,77, df=45, p=0.008). Prior to age correction, right caudate DAT binding was not statistically different (3.2±0.7 vs. 2.9±0.13, t=2.3, df=45, p=0.13) Regression analyses revealed a statistically significant effect of age on DAT binding in the left putamen (t=−2.55, df=45, p= 0.014) and the right caudate (t=−2.07, df=45, p= 0.045). To further understand the moderating effect of age on DAT findings, we adjusted for age using a linear correction to create DAT binding as if each subject was 30 years of age. The relationship between age and DAT binding was similar between ADHD and Controls in both right caudate and left putamen (interaction terms, p’s=NS). This analysis showed that DAT binding in the right caudate was15% (effect size 0.82) greater in adults with ADHD than in normal controls (t=7.7, df=45, p=0.008) ().
Because gender may also moderate DAT binding results (Mozley et al 2001
), we examined the influence of gender on DAT binding in the right caudate. This analysis showed that DAT binding in the right caudate was greater in females than in males (t=−3.24, df=44, p= 0.002) regardless of diagnostic status. When simultaneously controlling for sex and age, the differences in DAT binding in the right caudate were found to be somewhat larger than the original estimates (t=3.75, df=44, p<0.001). For example, DAT binding in the right caudate was 17% greater in male adults with ADHD (t=6.9, df=24, p=0.02) and 22% greater in female adults with ADHD than in normal controls (t=7.3, df=21, p=0.02).
In contrast, neither severity of ADHD, family history of ADHD, symptoms of anxiety and depression (Beck, Ham-A, Ham-D), nor ethnicity moderated DAT findings.