Sex differences in self-reported attention-deficit/hyperactivity disorder symptoms in clinical and population-based cohorts

Background Although the childhood prevalence of ADHD is higher in males than in females, some studies suggest that females report more severe impairment related to ADHD symptoms than males. The reason for this gender paradox is poorly understood. Here we explored sex differences in self-reported ADHD symptoms among adolescents and adults with and without an ADHD diagnosis across clinical and population-based Norwegian cohorts. Methods We analysed population-based data from the Norwegian Mother, Father, and Child Cohort Study (MoBa) (N = 90,816; 62% females, mean age 33.4 years), the youth@hordaland study (y@h) (N = 10,257; 53% females, mean age 17.4 years), and the ADHD in Norwegian Adults (ANA) project (N = 1677; 55% females, mean age 29.0 years). The Adult ADHD Self-Report Scale Screener (ASRS-6) was used as an outcome measure to define symptom severity of ADHD. Linear regression analyses were used to explore sex differences in ASRS-6 scores between individuals with and without a self-reported ADHD diagnosis (triangle). Age-adjusted, unstandardized regression coefficients (b) with 95% confidence intervals (CI) were reported. Results Participants with ADHD reported higher ASRS-6 scores than those without ADHD across all three cohorts. The ASRS-6 scores were highest in the youngest participants, particularly in females from the y@h cohort. The difference in ASRS-6 scores between those with and without an ADHD diagnosis was larger among females than males within all cohorts, at a statistically significant level both in y@h and ANA (MoBa: triangle females: b = 4.6 (95%CI 3.8; 5.4); triangle males: b = 4.2 (3.5; 5.0); y@h: triangle females: b = 5.1 (4.0; 6.2); triangle males: b = 3.2 (2.1; 4.2); ANA: triangle females: b = 8.6 (8.1; 9.2); triangle males: b = 6.5 (5.9; 7.2). Conclusions In both population-based and clinical cohorts, representing different age groups and study designs, we found a larger mean difference in reported ADHD symptoms between adolescents and adults with and without ADHD among females than males, suggesting barriers for females related to referral, assessment, and/or diagnosis of ADHD.