Welfare consequences for people diagnosed with attention deficit hyperactivity disorder (ADHD): A matched nationwide study in Denmark

The Danish Civil Registration System (CRS) was established in 1968, and all persons alive and living in Denmark were registered for administrative use. CRS includes individual information on the unique personal identification number, name, gender, date of birth, place of birth, citizenship, identity of parents and continuously updated information on vital status, place of residence and spouses. Since 1968, CRS has recorded current and historical information on all persons living in Denmark. Among persons born in Denmark in 1960 or later it contains complete information on maternal identity. For women born in Denmark in April 1935 or later it contains complete information on all their children. CRS contains complete information on immigrations and emigrations from 1969 onwards, permanent residence in a Danish municipality from 1971 onwards, and full address in Denmark from 1977 onwards. CRS in connection with other registers and biobanks will continue to provide the basis for significant knowledge relevant to the aetiological understanding and possible prevention of human diseases.

The Danish National Patient Register (NPR) was established in 1977, and it is considered to be the finest of its kind internationally. At the onset the register included information on inpatient in somatic wards. The content of the register has gradually been expanded, and since 2007 the register has included information on all patients in Danish hospitals. Although the NPR is overall a sound data source, both the content and the definitions of single variables have changed over time. Changes in the organisation and provision of health services may affect both the type and the completeness of registrations. The NPR is a unique data source. Researchers using the data should carefully consider potential fallacies in the data before drawing conclusions.

In spite of the growing literature about adult attention-deficit hyperactivity disorder (ADHD), relatively little is known about the prevalence and correlates of this disorder. To estimate the prevalence of adult ADHD and to identify its demographic correlates using meta-regression analysis. We used the MEDLINE, PsycLit and EMBASE databases as well as hand-searching to find relevant publications. The pooled prevalence of adult ADHD was 2.5% (95% CI 2.1-3.1). Gender and mean age, interacting with each other, were significantly related to prevalence of ADHD. Meta-regression analysis indicated that the proportion of participants with ADHD decreased with age when men and women were equally represented in the sample. Prevalence of ADHD in adults declines with age in the general population. We think, however, that the unclear validity of DSM-IV diagnostic criteria for this condition can lead to reduced prevalence rates by underestimation of the prevalence of adult ADHD.