Lay Summary

Using linked, individual level data from two nationwide Norwegian public registers we will investigate the presence of other mental, behavioral, and neurodevelopmental disorders in the population of children diagnosed with ADHD. We will describe patterns of comorbid diagnoses with ADHD, and consider its development over time. The findings will be relevant to clinicians, and will be informative in guiding future research.

Background

Attention-deficit/hyperactivity disorder (ADHD) commonly co-occurs with other mental, behavioral, and neurodevelopmental disorders such as learning disabilities, conduct disorder, anxiety, and depression. While comorbidity has been extensively studied, this research is often based on clinical samples. A valuable alternative approach is using registry data, which allows studying the complete population of interest. The Nordic countries are known for their extensive, high-quality public registers, providing complete and individual-level data for the entire populations. Consistent registration of personal identification number makes linkage between national registers possible. Due to the universal, single-provider health systems, patient data are essentially complete. Together, this offers a rare opportunity for conducting comprehensive longitudinal cohort studies of entire populations, with follow-up over several years and practically no attrition. Drawing on Norwegian registry data, our aim is to investigate patterns of psychiatric comorbidity in children diagnosed with ADHD on a population level. We will explore development over time, compare subgroups within the ADHD population, and contrast the ADHD population to a control sample from the general population.

Methods

We will use data from the Norwegian Patient Register (NPR) and the Norwegian Prescription Database (NorPD), two nationwide public registries that provide individual level data for the whole population. Our sample consists of all individuals aged 5-18 years that received an ADHD diagnosis in the Norwegian child and adolescent mental health services outpatient clinics during the years 2009 to 2011 (i.e., birth cohorts 1991–2006). The sample size is 9,360 individuals. Follow-up is until the end of 2020. Comorbid diagnoses will be categorized by section in ICD-10-chapter F01-F99 (i.e., 11 categories).

Results

As we have only recently received the full data material, analyses have yet to be ran at the time of the abstract submission deadline. Results will be presented at the conference.

Conclusion

The findings of this study will be relevant to clinicians working with this patient group, and will be informative in guiding future research.