Several limitations are noteworthy. First, DSM-IV criteria for ADHD were developed with children in mind and offer only limited guidance regarding adult diagnosis. Clinical studies make it clear that symptoms of ADHD are more heterogeneous and subtle in adults,36, 37
leading some researchers to suggest that assessment of adult ADHD might require an increase in the variety of symptoms assessed,38
reduction in the severity threshold,39
or reduction in the DSM-IV six-of-nine symptom requirement.40
To the extent that such changes would lead to a more valid assessment, our estimates of prevalence and related impairment will be conservative.
Second, adult ADHD was diagnosed based entirely on adult respondent self-report. Childhood ADHD is diagnosed largely from parent and teacher reports because children with ADHD have notoriously little insight into their symptoms.41
Use of informants is much more difficult for adults, though, making it necessary to rely on self-report.37
Methodological studies comparing adult self-reports versus informant reports of adult ADHD symptoms document the same general pattern of under-estimation as in child self-reports,42, 43
suggesting that prevalence is probably under-estimated here.
Third, the MI imputation model used to estimate ADHD in this study was based on a clinical assessment carried out only in the US. We have no way to confirm whether the calibration is as accurate in other countries. This is especially problematic given that little research on adult ADHD has been conducted outside of the US, making it unclear if the same markers apply in other countries. Given the centrality of this issue, it is important for structured assessment of adult ADHD to be expanded for use in future surveys and for the validity of these assessments to be evaluated in clinical reappraisal studies outside the US.
Within the context of these limitations, our results show adult ADHD to be a fairly common disorder in the labor force associated with substantial lost role performance. Our finding that the prevalence of ADHD is generally as high among workers as others was unexpected based on previous clinical research that has generally found patients with ADHD to have a high unemployment rate.18
However, disaggregation found that unemployed respondents have a higher prevalence of ADHD (5.5%) than working people (3.5%), while homemakers (1.9%) and students (2.2%) have the lowest rates.20
The finding that adult ADHD is significantly more prevalent among male than female workers is consistent with much previous general population research.18
The finding that ADHD is less prevalent among professionals than other workers is not surprising given that ADHD interferes with cognitive performance and might create a selection bias against success in professional work. The finding that ADHD is not related to age in the range considered here (i.e., 18–29 vs. 30–44) extends the broader finding that ADHD does not spontaneously remit in early adulthood.17
The finding that adult ADHD appears to be somewhat more prevalent in developed than developing countries could reflect the fact that the notion of a “deficit” existing in attentiveness has to be defined in relation to the level of environment demands on attention. A deficit exists only when demands exceed the person’s abilities. It might be that high environmental demands for attentiveness are more common in the workplaces of developed countries, leading to the higher recognition of adult ADHD in those countries. However, this possibility is only a speculation that should be confirmed with objective cognitive tests before it is accepted as true.
The key finding of the paper is that adult ADHD is associated with significant decrements in role performance. This finding is broadly consistent with much clinical evidence28
and with evidence from neuropsychological studies.44
The magnitude of the associations found here, though, are quite large in relation to comparable estimates reported in the literature for other chronic physical and mental disorders.45–47
It is noteworthy that we found more than half the days out of role associated with ADHD to be due to reduced quantity-quality of role performance rather than to days out of role. This is important from an employer perspective because many employers consider some number of days out of work (typically one per month) part of the cost of doing business and have mechanisms to reduce financial losses due to larger numbers of absence days (e.g., caps on paid sick days, disability insurance). However, employers typically expect their workers to be working when they are on the job. To find that most ADHD-related lost role performance occurs on days in role, then, is both striking and disturbing from an employer perspective.
Although we found statistically significant differences in ADHD prevalence across occupation, no between-occupation difference were found in the association between ADHD and role performance. Specifications involving other demographic variables were also generally not significant. These results suggest that the adverse effects of ADHD are widespread rather than concentrated among workers in jobs where high concentration is critical for success. The unusual finding that the association between ADHD and role performance is positive in the Netherlands is consequently difficult to explain and might be due to the low number of respondents or low estimated prevalence of ADHD in the Netherlands.
Our results regarding treatment of ADHD show clearly that adult ADHD is not recognized as a disorder that requires treatment in most of the countries studied. A much higher proportion of cases in the US and the Netherlands could be detected if professionals treating patients with other emotional problems screened for comorbid ADHD, as sizable minorities of ADHD cases in both countries receive treatment for other emotional problems. In the other countries, though, only small proportions of ADHD cases receive treatment for any emotional problem.
The above results raise the question whether adult ADHD is a candidate for targeted workplace screening and treatment programs. Short screening scales that are both sensitive and specific for adult ADHD exist.48, 49
It might be cost-effective from the employer perspective to implement workplace screening programs with such a scale to detect and provide treatment for workers with ADHD. The thinking here is that ADHD among workers has nontrivial prevalence, high impairment, and a low rate of treatment, whereas cost-effective therapies exist that are related to improvements in some objective aspects of role performance.50–52
The obvious next step from a public health perspective, given these findings is to evaluate the extent to which best-practices outreach and treatment would result in improvement in functioning that might have a positive return-on-investment for employers.