Discussion
This population-based study showed that an increased number of ADHD symptoms was associated with higher comorbidity, exposure to risk factors, and disability. Even low numbers of ADHD symptoms were associated with an increased burden of disease. These results confirm that ADHD is a dimensional trait in the general population. Concerning the distribution of ADHD symptoms and the associated sociodemographics, we found that 5.3% of subjects met the threshold of 4 or more symptoms on the ASRS screener, thereby having symptoms highly consistent with ADHD in adults. We further showed that a higher number of ADHD symptoms was significantly related to female gender, younger age, and living without a partner, suggesting that these characteristics may be considered risk factors for ADHD symptoms. No clear significant association was observed between two indicators of socioeconomic status (SES) and ADHD symptoms: educational level and job status (this showed a trend, p=0.06). This trend became significant when analyzing the association with the 4 ASRS strata instead of the association with the number of ADHD symptoms.. These findings coincide with earlier epidemiological reports among adults with ADHD or among adults with low numbers of ADHD symptoms (Bitter et al., 2010; Caci et al., 2014; Estevez et al., 2014; Fayyad et al., 2007; Polanczyk et al., 2010; Simon et al., 2009), with the exception of the relationship between female gender and ADHD symptoms. However, this gender difference was not present when comparing those with probable ADHD to those without probable ADHD, suggesting that females scored especially higher on a low numbers of symptoms.