Rising Prevalence and Incidence Trends in children and youth with ADHD in Ontario, Canada

by Dr. Debra Butt

Attention Deficit/Hyperactivity Disorder (ADHD) is a childhood-onset neurodevelopmental disorder. It is one of the most common childhood psychiatric conditions in Canada. ADHD is characterized by developmentally inappropriate symptoms of inattention, hyperactivity and/or impulsivity. This condition can impair academic, social, and/or occupational functions. For these reasons, it is important to conduct surveillance of ADHD trends over time for the purpose of planning for healthcare services and resources.

Yet, studies on the prevalence and incidence rates for ADHD in Canada have largely used case-finding algorithms applied to health administrative data that have not been adequately validated so it is unclear how accurate these algorithms are at detecting cases of ADHD. The aim of this study was to conduct a detailed validation study of administrative data algorithms to detect ADHD in children and youth aged 1-24 years from 2014-2021 with their full test characteristics, and then assess the performance of the top five administrative data algorithms for ADHD across Ontario, Canada.

We identified ADHD in administrative health data from case-finding algorithms using a reference standard of children and youth aged 1-24 years with known ADHD and without ADHD from their family physicians’ electronic medical records. We linked to health administrative data to test and validate multiple algorithms consisting of different combinations of physician billing claims, hospitalization diagnoses, emergency department visits, specialist consultation and/or prescription data to identify children and youth with ADHD within administrative data. These datasets were linked using unique encoded identifiers and analyzed at IC/ES in Toronto, Ontario, an independent, non-profit research institute funded by an annual grant from the Ontario Ministry of Health and Long-Term Care.

The optimal administrative data algorithm to detect ADHD was determined to be “2 physician visits for ADHD in 1 year or 1 ADHD-specific prescription” with a high degree of accuracy. It is also the only mental health case-finding algorithm in children and youth that performs well. From 2014, prevalence rates for ADHD in children and youth aged 1-24 years increased from 5.29 to 7.48 per 100 population in 2021. Males had higher prevalence rates (7.49 to 9.59 per 100 population, 1.3-fold increase) than females (2.96 to 5.26 per 100 population, 1.8-fold increase) from 2014-2021. Incidence rates increased from 2014 (0.53 per 100 population) until 2018, decreased in 2020 then rose steeply in 2021 (0.89 per 100 population, N = 34,013). Males also had higher incidence rates than females from 2014-2020 with females surpassing males in 2021 (0.70 to 0.81 per 100 male population,1.2-fold increase versus 0.36 to 0.97 per 100 female population, 2.7-fold increase).

In addition, we found that the observed prevalence rate for ADHD in children and youth in Ontario, Canada was lower than the expected prevalence rate in 2020 and this was mainly driven by the lower-than-expected prevalence rate in males in 2020 which persisted in 2021. Whereas in contrast, the observed prevalence rate in females was higher than expected in 2021. Similarly, the observed incidence rates compared to the expected rates overall and by sex, followed the same patterns as the prevalence rates from 2014-2021.

Therefore, our study developed and validated health administrative data algorithms to detect ADHD in children and youth aged 1-24 years. We determined an optimal administrative data algorithm for ADHD in children and youth with a high degree of accuracy and estimated prevalence and estimates rates from 2014-2021 in Ontario, Canada. Our findings suggest that prevalence rates for ADHD are increasing in both males and females and that incidence rates were highest among females in 2021 compared to males. We have a good quality case-finding algorithm for ADHD in children and youth derived from routinely collected health administrative data that can be used by epidemiologists in other provinces and across Canada, as well as health services researchers to make ADHD surveillance a mental health priority given its rising prevalence and incidence rates.