Geographic analysis of the variation in the incidence of ADHD in a country with free access to healthcare: a Danish cohort study

Abstract

BackgroundThe prevalence of citizens diagnosed with Attention Deficit Hyperactivity Disorder (ADHD) has risen dramatically over the past decades in many countries, however, with large variations. Countries such as Denmark with centrally organized well fare systems, free access to health services and individual tracking based on unique personal identification may in particular contribute to our understanding of the reasons for this increase. Based on Danish registers we aimed to examine the geographical patterns of the distribution of ADHD diagnosis and medication use and explore the association with access to diagnostic services, diagnostic culture, neighbourhood socioeconomic status and municipal spending on health care for children.MethodsWe combined information on registered diagnosis of ICD-10 Hyperkinetic Disorder and ADHD medication use in a Danish register-based cohort of children born between 1990 and 2000. We mapped incidence proportions of diagnoses and medication use within the 98 Danish Municipalities. Global and local clustering of ADHD was identified using spatial analysis. Information on contextual factors in the municipalities was obtained from national registers. The associations between the incidence of ADHD and contextual factors were analysed using Bayesian spatial regression models.ResultsWe found a considerable variation in the incidence of ADHD across the municipalities. Significant clustering of both high and low incidence of ADHD was identified and mapped using the local Moran’s I. Clustering of low incidence of diagnosis and medication use was observed in less populated areas with limited diagnostic resources and in contrast clustering of high incidence in densely populated areas and greater diagnostic resources. When considering the spatial autocorrelation between neighbouring municipalities, no significant associations were found between ADHD and access to diagnostic services, different diagnostic culture, socioeconomic status at municipality level or the municipal spending on health care for children.ConclusionsA large geographical variation of ADHD in the municipalities was observed despite tax-financed and free access to healthcare. Although not statistically significant, results indicate that accessibility to diagnostic resources might explain some of the variation in ADHD incidence. In contrast to US studies the observed variation was not statistically associated to contextual factors in terms of SES, municipal spending on health care for children or differences in diagnostic practices.

Life Span Studies of ADHD—Conceptual Challenges and Predictors of Persistence and Outcome

“…The finding that ADHD treatment is a risk factor for persistence is not surprising, since the most severe cases are selected for treatment. Barriers to health care may influence this finding; lack of access to treatment might be a marker of environmental or socioeconomic risk factors (e.g., ethnic minorities or living in an area with limited resources [49, 50]). Importantly, the two studies that found the effect of ADHD treatment adjusted their findings for disorder severity, but possibly, the treatment-severity relationship was not fully captured by the instruments used.…”

The influence of participation in target-shooting sport for children with inattentive, hyperactive and impulsive symptoms – A controlled study of best practice

“…Approximately 2–3% of children attending Danish schools are diagnosed with ADHD [2, 3], and worldwide the population prevalence of ADHD is 5% [4]. Many children with ADHD experience difficulties in managing social relations, and are often excluded from participating in leisure activities with other children, e.g.…”

Temporal trends and geographical variability of the prevalence and incidence of attention deficit/hyperactivity disorder diagnoses among children in Catalonia, Spain

“…ADHD incidence in children was also assessed in some studies 8,[12][13][14][15] . Only few studies have reported annual incidence estimates of diagnosed ADHD for an extensive period of time allowing for time trend analysis, but most of them showed an increase in the incidence during the study period [13][14][15] . Overall, higher incidence was detected in boys and ADHD diagnosis for both boys and girls was greater in children aged 6-11years 14 and specially among 7-9 years old 13 .…”