The Effect of ADHD on Educational Outcomes
In recent years, Attention Deficit Hyperactivity Disorder (ADHD) has been a subject of increasing public attention and concern. Affecting an estimated 4 to 5 percent of children, ADHD is the most common chronic mental health problem among young children in the U.S.
ADHD is characterized by an inability to pay attention, hyperactivity, or both. A formal diagnosis of ADHD is based on exhibiting these behaviors to a degree that is inconsistent with the child's development level, in multiple settings, and over a prolonged period of time. ADHD is typically treated with drug therapy (often stimulants such as Ritalin) or psychiatric counseling. Much of the controversy over ADHD has focused on whether it has been under or over diagnosed and treated.
Despite the concern about ADHD, there are relatively few studies of its effect on children's educational outcomes. Janet Currie and Mark Stabile explore this subject in "Child Mental Health and Human Capital Accumulation: The Case of ADHD" (NBER Working Paper 10435).
The authors use data on children aged 4 to 14 in the 1990s from the U.S. National Longitudinal Survey of Youth and the Canadian National Longitudinal Survey of Children and Youth. They focus on a continuous measure of symptoms from an ADHD screening test administered to all children rather than reported cases of ADHD to avoid the problem of imperfect diagnosis and to examine the effect of lower levels of symptoms. They also use diagnoses from two sources, the child's parents and teacher, to better measure the child's true level of ADHD.
The authors pay particular attention to the possibility that some children - for example, those in low-income households - may be more likely to have ADHD and also more likely to have worse outcomes, which could confound estimates of the effect of ADHD on outcomes. To address this, they control for factors such as family income and mother's education in their analysis. They also estimate models comparing differences in outcomes among siblings with different levels of ADHD symptoms, to control for the effect of any household-level factors that are not observable in the data.
The authors find that children with more symptoms of ADHD - such as being impulsive or restless - have significantly lower math and reading scores on standardized tests several years later. These children also have an increased probability of grade repetition, enrollment in special education, and delinquency, which includes behaviors such as stealing, hitting people, or using drugs. The results are similar for U.S. and Canadian children.
The magnitude of these effects is large. For example, being in the top 10 percent of the ADHD symptom distribution (which may correspond roughly to having ADHD), is estimated to nearly double the probability of grade repetition and to lower math and reading test scores by 8 to 10 percent relative to average test scores for U.S. children. Strikingly, the effects of ADHD on child outcomes are much larger than the effects of physical health problems such as having asthma or being in poor health.
Interestingly, the authors find that experiencing an additional symptom of ADHD is associated with a similar deterioration in outcomes both for children with low and high levels of ADHD symptoms. This suggests to the authors that "even children with scores low enough that they would never be diagnosed with ADHD may nonetheless suffer ill effects of behaviors associated with the disorder."
As boys are two to three times more likely to suffer from ADHD than girls, it is interesting to compare whether the effects of ADHD on outcomes differ by gender. The authors find that the boys and girls with moderate symptoms are similarly affected, but that boys with severe symptoms are much more likely to be enrolled in special education and to have lower test scores than comparable girls.
The authors also examine whether the effects of ADHD and treatment for the disorder vary by income level. The find that children in high-income families are less likely to be retained in grade, but are otherwise similarly affected by ADHD symptoms as children in low-income families. Surprisingly, children in high-income families are no more likely to be treated for ADHD, in stark contrast with treatments for physical health problems. The authors suggest that low-income families may have access to ADHD treatment through Medicaid or school referrals or that high-income families may avoid treatment for ADHD due to perceived stigma.
The authors conclude that "the severity of problems associated with ADHD and the pervasiveness of its symptoms suggest that efforts to find better ways to teach the relatively small number of children diagnosed with ADHD could have a larger payoff in terms of improving the academic outcomes of many children with milder symptoms."
The authors acknowledge financial support from the Social Science and Humanities Research Council of Canada, Princeton University's Center for Health and Well-Being, and the Candian Institutes for Health Research. This research was summarized by Courtney Coile.