Geographic variation in the prevalence of ADHD

ADHD is the most commonly diagnosed childhood behavioural disorder in most countries, including in Denmark. A recent review suggests a worldwide-pooled prevalence of ADHD of about 3.4%. However, the prevalence of the ADHD diagnosis and the use of prescribed ADHD medications vary largely between and within countries. We investigated the geographical variation in the incidence proportion of ADHD diagnosis and prescribed ADHD medication in a cohort of all Danish children born from 1990-2000. Great variations were found between the Danish municipalities in the incidence of ADHD diagnoses (a) and prescribed ADHD medication (b) as shown in the maps in Figure 1. We found a mean incidence proportion of both ADHD diagnosis and prescribed medication of 1.19%, which ranged from a low of 0% to a high of 2.87% in the Danish municipalities. The incidence of ADHD diagnoses and prescribed medications seems largely dependent on the diagnostic resources available (shown as red dots in map a and c). We found clustering of low incidence of ADHD in less populated areas and clustering of high incidence in densely populated areas.     

Figure 1. Incidence proportion (%) in children aged 0-11 years born from 1990-2000 of (a) diagnosis, (b) medication use, (c) medication use and no registered diagnosis and (d) overall ADHD by municipality. The incidence proportions are split into quartiles. Red points in map (a) and (c), respectively, show the public and private diagnostic facilities in the municipalities (Madsen KB, Ersbøll AK, Olsen J, Parner E, Obel C. Geographic analysis of the variation in the incidence of ADHD in a country with free access to healthcare: a Danish cohort study. International Journal of Health Geographics. 2015; 14: 24.)

This project was part of a PhD dissertation finalized in June 2017 (defense is expected in September 2017)