A recent article in the Journal of child Psychology and Psychiatry examined the long term course of ADHD and co-morbid diagnoses among boys and girls as they transitioned from childhood into adolescence. The vast majority of research on ADHD has been done with boys, mostly due to the sex difference in the rates of ADHD. The few studies that have included girls have shown significant differences between boys and girls in a number of domains, including the physiological correlates of the condition, cognitive function, and co-morbidities. Yet, we know little of the longitudinal progression of ADHD in girls. Specifically, it is unknown whether the course of ADHD is similar in boys and girls or whether they have similar co-morbid conditions throughout childhood and adolescence.
The authors of the Journal of Child Psychology and Psychiatry study examined participants from two independent longitudinal studies of ADHD. The first study started in the 1980s and included 140 6-to-17 year-old boys with ADHD, 206 siblings, 280 parents, and 120 non-ADHD peers. These kids were assessed for up to 10 years after the initiation of the study. The second study started in 1993 and included 140 6-to-17 year-old girls, 183 siblings, 274 parents, and 122 non-ADHD peers. These girls were followed for up to 5 years. The final sample for the study included 143 ADHD girls and 147 ADHD boys. Both groups were on average approximately 11 years old at the time of the first assessment. However boys were significantly older (mean age 19) at the time of the last followup compared to the girls (mean age 16).
The ADHD diagnoses were obtained via a 3-step procedure that included a comprehensive psychiatric interview. This greatly limits the possibility that some of the ADHD cases included in the study were misdiagnoses. An similar assessment of ADHD symptoms and co-morbid conditions were conducted during the follow up period.
1. As you can see from the graphic below, the authors found that ADHD symptoms decline with age in a non-linear fashion. Specifically, the decline in symptoms accelerates with age.
2. As also noted in the graphic below, girls had significantly more ADHD symptoms than boys across all developmental periods. While in the graphic it looks like this difference was more pronounced during early childhood, the statistical analysis conducted indicated that the sex difference in ADHD symptoms was consistent (the same) at all ages.
3. The authors also found a sex difference in the developmental progression of co-morbid conditions. Specifically, while in childhood ADHD in boys and girls were associated with the same co-morbid conditions (Mood Disorders, Disruptive Behavior Disorders, and Anxiety), during adolescence ADHD was no longer associated with anxiety for boys. In contrast, girls continued to show high co-morbidity between ADHD and anxiety in adolescence.
The good news is that ADHD symptoms appear to decrease with age, and that this decline accelerates as children get older. However, the news are not as good for girls. The study shows that symptoms in girls appear to be more severe than in boys, and that for girls there are more co-morbid conditions during adolescence than for boys. While this may suggest that ADHD is more severe in girls than in boys, we should keep in mind that the results of any study is highly dependent on the sample used, and more importantly the way participants were recruited. For example, boys and girls in this study came from two independent samples, and unknown methodological differences between these samples could be driving some of the results. In addition all of the participants with ADHD were initially included after getting a clinical diagnosis for ADHD by a referral source, which was later confirmed by the study’s own clinician (details on how the recruitment took place were not provided). Therefore, it is possible that these findings reflect sex differences in the initial clinical identification of ADHD by the kid’s clinicians. Specifically, it is possible that girls who were diagnosed and subsequently entered the study simply did so because of experiencing more severe symptoms. While indeed there are some methodological limitations, this is one of the only studies who have provided comprehensive empirical data that help us understand the differences between boys and girls in the progression of ADHD symptoms and co-morbid conditions during childhood and adolescence.
The reference: Monuteaux, M., Mick, E., Faraone, S., & Biederman, J. (2009). The influence of sex on the course and psychiatric correlates of ADHD from childhood to adolescence: A longitudinal study Journal of Child Psychology and Psychiatry DOI: 10.1111/j.1469-7610.2009.02152.x
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