The relationship between ADHD and performance on IQ tests

People with ADHD (Attention Deficit Hyperactivity Disorder) often perform worse on IQ (Intelligence Quotient) tests compared to individuals without the disorder. Below are some findings from studies investigating this relationship:

1. Neuropsychological Performance and ADHD Symptoms: Children with ADHD tend to perform below average on neuropsychological tests that measure executive functions such as sustained attention, response inhibition, and working memory. These deficits are particularly evident in tests that require free recall/retrieval, which depends on intact functioning of the frontal regions of the brain  (Muir-Broaddus et al., 2002) .
2. Relationship between ADHD and Performance on IQ Tests: Study with 326 children with ADHD showed that those with higher IQ (≥120) tend to perform better on continuous tests of visual and auditory performance compared to children with average IQ (70- 120). However, even with high IQ, these children still showed deficits in some areas, suggesting that the categorization of continuous performance tests should consider IQ  (Park et al., 2011) .
3. Impact of ADHD Symptoms on Intellectual Performance: A study focused on Icelandic inmates with ADHD indicated that ADHD symptoms in adults negatively affect performance on intellectual tests, regardless of test completion time. ADHD symptoms in adulthood significantly impair intellectual performance  (Goodwin et al., 2011) .
4. Masking of Cognitive Deficits by High IQ: Adults with ADHD and high IQ may show less evidence of deficits in executive functions compared to those with standard IQ. This suggests that higher IQ may compensate for deficits in executive functions, complicating the accurate diagnosis of ADHD  (Milioni et al., 2017) .
5. Performance Differences on IQ Tests: A meta-analytic study found that adults with ADHD score lower on WAIS intelligence tests compared to adults without ADHD. However, this difference was considered small and without relevant clinical significance, suggesting that only a subset of adults with ADHD may have lower general intellectual abilities  (Bridgett & Walker, 2006) .

In summary, individuals with ADHD often perform poorly on IQ tests, especially in areas that require executive functions, although some variables such as high IQ may mask these deficits. This conclusion is supported by multiple studies that highlight the relationship between ADHD and performance on IQ tests.

ANTSHEL, K. et al. High IQ May “Mask” the Diagnosis of ADHD by Compensating for Deficits in Executive Functions in Treatment-Naïve Adults With ADHD. *Journal of Attention Disorders*, v. 21, no. 5, p. 455-464, 2017. 

BRIDGETT, DJ; WALKER, M. Intellectual functioning in adults with ADHD: a meta-analytic examination of full scale IQ differences between adults with and without ADHD. *Psychological Assessment*, v. 18, no. 1, p. 1-14, 2006. 

GOODWIN, EJ et al. The impact of ADHD symptoms on intelligence test achievement and speed of performance. *Personality and Individual Differences*, v. 50, p. 1273-1277, 2011. 

MUIR-BROADDUS, J. et al. Neuropsychological test performance of children with ADHD relative to test norms and parental behavioral ratings. *Archives of Clinical Neuropsychology*, v. 17, no. 7, p. 671-689, 2002. 

PARK, MH et al. Differences in Performance of ADHD Children on a Visual and Auditory Continuous Performance Test according to IQ. *Psychiatry Investigation*, v. 8, no. 3, p. 227-233, 2011.