“…Our main aim was to evaluate psychiatric comorbidity in adults with ADHD, and for this analysis, no confounding variables are relevant; thus, we only adjusted for age (birth year; 5‐year groups from 1967 to 1997, with 1967–1973 as the reference period). To evaluate how risk factors for both ADHD and other psychiatric disorders influenced the prevalence ratios, we ran two regression models, including the following covariates that all have been documented as risk factors for ADHD and psychiatric disorders : Model 1: birth year, maternal marital status (single, married/cohabiting (reference category), other), maternal age (<20, 20–24, 25–29 (reference value), 30–34, 35–39, 40+) and paternal age (<20, 20–24, 25–29, 30–34 (reference value), 35–39, 40–44, 45–49, 50+) at delivery, parent's highest attained educational level at record linkage (low (<10 years of education), middle (10–12 years of education) and high level (>12 years of education (reference category)), the individual's gestational age in weeks (<27, 28–31, 32–34, 35–36, 37–41 (reference value), 42+) and gestational age‐ and sex‐specific birthweight z‐scores (<‐2.0; −2.0 to −0.51; −0.5 to 0.5 (reference value); 0.51 to 2.0; 2.01+).…”