The results of this large longitudinal register-based study of young adults in Sweden suggest that individuals with ADHD are at increased risk of the co-occurrence of low education and unemployment. Clustering of these indicators of social disadvantage was stronger the longer the unemployment had lasted. Clustering also seemed to be more pronounced among women than men and strengthened over time. An analysis among people with ADHD further indicated that low education separately clustered with unemployment and with new-onset disability pension.
To our knowledge, this is the first study investigating clustering of ADHD and social disadvantage in young adulthood. Our findings are in line with previous investigations which have shown associations of ADHD with poor educational attainment and unemployment [7–12]. One study suggested that poor educational attainment may actually be the link between ADHD and unsuccessful labour market outcomes . Other studies have shown that accumulated social disadvantage in childhood environment, such as financial difficulties, are associated with a higher risk of ADHD [16, 17]. Our results add to these findings by showing that social disadvantage may continue accumulating throughout young adulthood among individuals with ADHD.
Our findings suggest that the clustering of ADHD, low education and unemployment may increase over time. Because the study cohort comprised young adults, some of them might have ongoing education. However, information was not available to show if some of them completed schooling during follow-up. However, it is more likely that individuals with ADHD were those who dropped out of school, thus, the clustering estimates may be underestimates of the actual levels of clustering.
We also found that in this cohort, the clustering was stronger among women (4.71 at baseline; 6.62 at follow-up) than men (3.71 at baseline; 5.28 at follow-up). This is a novel finding which needs to be explored in further studies. The prevalence of ADHD is higher among men than women and there are also sex-differences in the symptom profiles. Women tend to demonstrate more inattention-type symptomatology whereas symptoms among men are typically characterized by externalizing behaviour, such as hyperactivity or impulsivity . Because inattention-type symptoms are less evident in classroom settings than e.g., hyperactivity and impulsivity, girls are less likely to be referred to healthcare services and are typically diagnosed later than boys . This may reduce their possibilities to receive effective, early treatment interventions. There is also some evidence that women with ADHD have a higher risk of developing substance abuse disorders than men with ADHD . ADHD is also associated with early single parenthood  which is more common among women than men with ADHD [19, 20]. This may further reduce these young women’s opportunities in education and paid work.
When we restricted the data to individuals with ADHD, we found that at follow-up, a combination of having low education and disability pension without unemployment was clustered (O/E ratio = 1.62). Similarly, a combination of having low education and unemployment without disability pension was clustered (O/E ratio = 1.17). Having all three in combination was less likely than expected (O/E ratio = 0.84). These findings can be interpreted from the social security system perspective. If a person is granted a disability pension or is long-term sickness absent from work for a long period of time, it is less likely that he/she seeks unemployment benefits. Moreover, individuals with ADHD who receive unemployment benefits are probably fit enough to continue seeking job and do not claim for disability pension. However, there was also clustering of advantage among individuals with ADHD; the observed prevalence of having none of the three (low education, unemployment and disability pension) was greater than the expected prevalence. Thus, higher education may protect young adults with ADHD from early labour market marginalization. A previous study has shown that the association between externalizing problems and high-school drop-out may be mediated by poor school grades . Individuals with ADHD and high education may also represent those with high functional capacity enabling them to attain higher education. It is also possible that high education gives them means to cope and adapt to work-related demands.
Strengths and limitations
The strengths of our study include high-quality detailed register data that cover the entire population in Sweden and a prospective study design which allowed us to examine how clustering of social disadvantage changes over time. The Swedish healthcare registers have been proven to have good coverage and high validity  although the coverage of outpatient care was not completely accurate during the first years of observation. The used healthcare data include specialised inpatient and outpatient healthcare, that is, secondary care, but not primary healthcare. It means that children and young adults diagnosed in primary health care are not included. However, most would at least at some point in the disease trajectory have had assessment and/or treatment in specialized care. Further studies could also include diagnosis-specific disability pension to examine whether mood disorders are the main diagnoses of disability in ADHD . Finally, further research is needed to examine the generalisability of our findings to other countries with different social security and health care systems.