Three questions are frequently asked regarding the relationship between intelligence and ADHD. One, does the population of individuals with ADHD represent a normal distribution in terms of intellectual skills? Two, are there characteristics unique to children with ADHD demonstrating superior or better intellectual abilities? Three, are there similar or different characteristics of ADHD in those demonstrating deficient intellectual abilities. In this month’s article, I will briefly review the literature on intelligence and ADHD and address these three important questions.
It is likely that ADHD has a uni-directional effect on intelligence in a number of ways. The impact of limited self-control and impaired sustained attention may well, to a small degree, diminish the acquisition of intellectual skills. However, to a larger degree ADHD is likely to interfere with the application of skills and the efficient test taking strategies necessary to perform well on intelligence tests. Researchers have found a link between IQ and ADHD as well as a link between IQ and other types of behavioral problems. Rates of hyperactive-impulsive behavior and measures of intelligence appear to have a negative association. In contrast, association between ratings of conduct problems and intelligence are often much smaller, in some cases, non-significant. When hyperactive-impulsive behavior is controlled, the relationship among verbal I.Q., achievement and disruptive behavior appears to be relatively specific to the hyperactive-impulsive element observed in disruptive behavior disorders. When efforts are not made to control for I.Q., samples of children with ADHD do differ significantly from controls, particularly demonstrating lower verbal intelligence. It has been suggested that this difference is consistent with a theoretical model of ADHD as noted by Dr. Russell Barkley, reflecting a disorder of poor impulse control.
Measures of sustained attention and inhibition are associated to a small but significant degree with measures of intelligence. Matching subjects with ADHD with controls and statistically controlling for I.Q. differences appears to reduce or eliminate the effects of ADHD upon intelligence. Group differences in Verbal I.Q. should not be viewed as an artifact of group selection nor as a source of error to be removed. These differences may in fact reflect real differences in the two populations. The preponderance of the data suggests, however, that less than 10% of the variance in Verbal I.Q. is accounted for by ADHD. Thus, the population of individuals with ADHD generally falls along a normal distribution in terms of intellectual skills. One might expect that 3% to 5% of those with gifted intellect will meet the symptom criteria for ADHD.
In contrast, the impact ADHD has on the efficient use of intellectual skills is likely greater. This phenomenon, however, is nearly impossible to evaluate given the idiosyncratic differences in children and their responses to differing environmental circumstances. Once again it is reasonable to conclude that children with ADHD demonstrate a generally normal distribution of intellectual skills. However, due to their poor self-control, assessment at any give moment may yield underestimates of their intellectual abilities, particularly on tasks requiring inhibition. Attention problems have been reported as quite common in the intellectually handicapped population, a problem that should not be thought to skew this bell curve but rather likely reflects the fact that a variety of neurological problems can lead to symptoms of hyperactivity, inattention and impulsivity.
I believe the research in this area is well-grounded, and has been generated and replicated over a twelve to fifteen-year span. Why then does it continue to be suggested anecdotally that children with ADHD fall inordinately at the higher end of the intellectual distribution? Why then has it been suggested that ADHD, specifically problems with impulsivity, may reflect some form of dysfunctional creativity? Viewing impulsivity as a potentially positive symptom attribute of ADHD may be a means of influencing the general public’s view of the disorder as somehow beneficial. Scientifically, this quality is and continues to be a significant liability. There is no scientific data to suggest that children with ADHD are more intelligent nor creative. Their impulsivity may result in their being quicker to offer suggestions and ideas and in some circumstances, this may result in adults perceiving them as more creative. The idea that children with ADHD attend to different aspects in their environment, resulting in their gathering and using more diverse information is simply unsubstantiated.
A number of writers have argued that the overlap between creativity and ADHD results from the fact that creative individuals may be sensation seeking. Some have suggested that a significant proportion of children diagnosed with ADHD are in fact simply intelligent, creative and bored! Yet, no data has been provided to support this hypothesis.
The preponderance of the data argues that intellectual processes are generally independent from ADHD. Although children with ADHD may perform inconsistently or deficiently on measures of intellectual skill, this should not lead one to assume that deficiencies in intellect, or for that matter, inconsistencies in intellectual performance are diagnostic of ADHD. Though it may be the case that intelligence is a protective factor and for some individuals with ADHD may serve to insulate them from the adversity of the condition, intelligence clearly falls far short of protecting someone with ADHD from the adverse experiences observed and reported at home, school and on the playground. It is time we put aside the notion that individuals with ADHD are smarter than the rest of us or for that matter, simply misdiagnosed geniuses bored with the repetitive, “bland educational environment we have created.”
