Dr Berg raises the possibility that respondents in our surveys who reported persistence of ADHD in adulthood might actually have had symptoms caused by some other disorders, such as alcoholism, that are more stigmatising and less likely to be treated than ADHD. Such respondents might consciously have provided incorrect information in an effort to avoid stigma and to increase their chances of receiving treatment. Dr Berg states that such machinations occur in his country. This is an important point in view of the stigma associated with mental disorders and the fact that some healthcare systems discriminate against certain diagnoses. Mental health professionals need to increase their efforts to raise awareness and address these problems.

That said, it strikes us as implausible that our findings are importantly affected by the sort of bias proposed by Dr Berg. First, the World Mental Health surveys are community epidemiological surveys in which no treatment is provided. Second, in a number of the participating countries ADHD is not commonly recognised as an illness, making it unlikely that community respondents would have the sophistication to seek out this diagnosis. Third, we carried out in-depth clinical reappraisal interviews with a probability sub-sample of respondents who reported adult persistence of ADHD. We excluded respondents if concerns existed that another diagnosis might be primary. Although it is possible that some respondents were so familiar with ADHD that they tricked our experienced clinical interviewers, we consider it unlikely that this was widespread. Fourth, treatment-seeking was low in most World Mental Health surveys. When it occurred, the reason for seeking treatment was not ADHD but a comorbid disorder.

Irrespective of whether the type of bias Dr Berg suggested exists in epidemiological surveys, our results imply that clinicians should look more seriously for ADHD in their adult patients than they have before. As more physicians screen for ADHD among adults presenting for treatment of other psychiatric disorders, the extent to which untreated adult ADHD exists among help-seekers will become apparent.