Dr. Robert McKeown, distinguished professor emeritus in the department of epidemiology and biostatistics at the University of South Carolina Arnold School of Public Health, has recently published two collaborative studies on the symptoms and trends of attention deficit/hyperactivity disorder (ADHD) based on his long-term research.
[Photo: Dr. Robert McKeown]
The first study, published in the Journal of Attention Disorders, followed a sample of children from elementary to high school through a 10-year, South Carolina-based project funded by the Centers for Disease Control and Prevention (CDC) entitled Project to Learn about ADHD in Youth (SC PLAY). The researchers found that the persistence of ADHD symptoms over time varies depending on the category of the symptom. Inattentive symptoms tended to persist through adolescence while hyperactive/impulsive symptoms were more likely to diminish in number. Although boys were inclined to have a higher number of symptoms, the pattern of persisting or diminishing symptoms held true for both boys and girls. “These findings help clinicians, who are seeing increasing numbers of older adolescents and adults presenting with ADHD symptoms, understand how the presentation of ADHD may change over time in children of different ages and in adults,” says Dr. McKeown. The researchers’ conclusions also reveal how maturation and the adoption of coping skills may influence how individuals with ADHD may experience symptoms over time.
The second study, published in the Journal of the American Academy of Child & Adolescent Psychiatry, combined the data from the first study with data from a second funded site in Oklahoma (OK PLAY) to examine how ADHD prevalence estimates were impacted by changing the criteria or case definition. For this study, the researchers wanted to determine the variation in ADHD prevalence when limitations resulted in less rigorous case definitions as well as assess the impact of newly updated ADHD diagnostic criteria. The team’s findings suggest that one of the recent diagnostic criteria modifications,, changing the minimum age for presentation of symptoms from seven to 12, resulted in a substantial increase in the prevalence of children who met criteria. On the other hand, the new criterion requiring only five symptoms for those aged 17 and older instead of six resulted in a very small increase in the prevalence estimate.
Researchers collect information on ADHD using a variety of approaches, each with their own data limitations, and clinicians are especially limited by time and resource constraints. Scientists have long suspected that these methodological challenges impact the resulting estimates of ADHD prevalence and trends. These findings assist researchers by actually quantifying the effects of modifying the criteria and help differentiate trends in prevalence estimates that may be due to changes in diagnostic criteria or research limitations from trends that represent real changes in the prevalence of the disorder.