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Measuring Intelligence in Autism

Marina Sarris
Interactive Autism Network at Kennedy Krieger Institute
Date Published: 
October 20, 2015

Photo illustration of blocks spelling ASD for article on autism spectrum disorder and IQIntelligence is a touchy, and complicated, subject when it comes to autism. When Dr. Leo Kanner first described the condition he named autism 70 years ago, he noted that some children he examined were thought to be intellectually disabled, although he suspected otherwise. Their social, communication and behavior problems gave them the appearance of intellectual disability to a world as-yet unaware of autism's existence.

Even today, autism itself can make it hard to test a child's intellectual ability. Imagine a young boy with poor language skills who prefers sameness and cannot tolerate fluorescent lights, all characteristics of autism spectrum disorder (ASD). Place him in a brightly-lit office with an IQ examiner – a stranger – asking him to do things he doesn't understand. Will he perform at his best, that is, assuming he can complete the test?

Almost 10 years ago, when the Interactive Autism Network (IAN) began collecting research data from families, it faced a problem when it came to reporting on the intelligence of children with autism. One in 10 children in IAN had been diagnosed with intellectual disability (ID), but more than twice that many had an intelligence quotient (IQ) score of 70 or less, according to their parents.1 On most IQ tests, a score of 100 is considered standard (essentially, average), and a score of 70 or below suggests intellectual disability.

What did that mean? When IAN delved deeper, it discovered that some parents doubted the accuracy of their children’s intelligence testing.1 Their children either couldn't complete the test due to behavioral problems, or received widely different scores on different occasions. In those cases, which score was right?

When American psychiatrists updated their diagnostic manual in 2013, they acknowledged a difficulty with IQ tests and autism. Although the manual says intellectual disability is common in autism, it cautions that measuring a child's intellectual ability may be complicated by the symptoms of autism itself. The manual also says, "IQ scores in autism spectrum disorder may be unstable, particularly in early childhood."2 In other words, a child's score may vary widely over time.

What is intelligence and intellectual disability?

Drawing of psychologist Alfred Binet, from Wikimedia CommonsWhen French psychologist Alfred Binet developed the first modern IQ test in the early 1900s, its purpose was to find children who needed special education help. Binet never intended the IQ score to be a measure of intelligence, a concept "too complex to capture with a single number," according to evolutionary biologist Stephen Jay Gould in The Mismeasure of Man.3

IQ tests have changed since then. Common tests now include the Stanford–Binet Intelligence Scale, which bears the name of the early pioneer, and the Wechsler ScaIes. Such tests measure skills that are generally important for success in school. Psychologists often include them in the battery of tests given to people suspected of having a learning disability or developmental disorder.

But IQ tests measure only a part of what we often think of as intelligence, which includes a person's ability to solve problems, reason, plan, think abstractly, and learn from the world around him.

When determining if someone has intellectual disability, doctors should look at more than just IQ, according to the psychiatric diagnosis manual. They also should consider adaptive functioning, that is, how well the person performs skills necessary for everyday life.2

"Adaptive behavior encompasses the set of skills that help an individual have personal independence," explained Amie Duncan Ph.D., a psychologist at Cincinnati Children's Hospital Medical Center who has researched the topic.

Adaptive skills include the ability to bathe oneself, take medicine properly, prepare a sandwich, cross the street safely, communicate important information, and take a bus to work, among many other things. Adaptive skills vary according to a person's age and culture.

Generally, adaptive skills track with IQ. Someone with average IQ would be expected to have average adaptive skills. However, in autism, researchers have found that adaptive skills may lag behind IQ, sometimes far behind.

Problems with daily living skills "may be especially prominent in those with higher cognitive abilities" and autism, according to a study by Dr. Duncan and others.4 That study included 417 adolescents with ASD in the Simons Simplex Collection research project. Half of them had daily living skills that were "significantly below" expectations for someone of their age and IQ. About a fourth of them had adaptive skills similar to people with mild to moderate intellectual disability, even though their IQ scores were much higher.

That disconnect between IQ and adaptive skills may be frustrating for some with ASD. Other people may not understand why someone with his or her "book smarts" struggles with seemingly easier skills, such as personal hygiene, asking for help, or getting places on time.

Often IQ is used to separate "low-functioning autism" from "high-functioning autism,"5 but those labels can be crude. Someone with intellectual disability – and good adaptive skills – may hold down a job and function at a higher level than someone with an average IQ who does not work or leave his home, says Dr. Peter Gerhardt, a behavior expert.6

The Rain Man Phenomenon

The mix of ability and disability in autism took extreme form in the 1988 movie Rain Man. The fictional Rain Man, played by Dustin Hoffman, has extraordinary memory and calculation skills, along with significant challenges from autism. He can memorize a phone book and instantly count scores of toothpicks, but he also believes a candy bar and a car each cost "about $100." Moviegoers were fascinated by those rare people who have seemingly superhuman brain skills along with borderline or low IQs.

Doctors have long been aware of that rare condition, called savantism. Researchers at Yale University described one such "autistic savant;" Donny could calculate the day of the week in which someone was born in less than a second.7 Music is another area where autism may confer an advantage, at least in some people. People with autism appear to be more likely to have perfect musical pitch – or some version of it – than the general population, according to several studies.8-13 Some scientists wonder: Is there something about the autistic brain that allows extreme ability to flourish amid significant disability? That question remains the subject of study.

Most people with autism lie somewhere between the extremes of severe intellectual disability and genius, along a spectrum of abilities. No one knows why autism affects people differently, at least not yet. But researchers do know that, as a group, the IQs of people with ASD have changed dramatically over time, as has their understanding of autism itself.

Increasing IQs in Autism

Photo illustrating boy with autism using picture cards for testing from iStockFrom 1966 to 1998, studies found that about only one-fifth of the people with ASD functioned in the "normal range" of intelligence, according to a 1999 review.14 But years later, in 2014, a U.S. study found that almost half of the children with ASD had average or above average intelligence, that is, an IQ score above 85. Less than a third of the children with autism had intellectual disability, and 23% had IQ scores in the "borderline range" from 71 to 85.15

What explains the collective increase in IQ scores among people with autism?

Many say the change reflects the expansion of the diagnosis to include people with milder forms of autism, such as Asperger's Syndrome, in the 1990s. People with Asperger's did not have speech or cognitive delays in early childhood. "It may be the case that historical data do not apply to children who are currently receiving an ASD diagnosis," according to a 2011 report in Brain Research.16

Another factor at play: the spread and success of intensive early intervention programs for toddlers and preschoolers with autism. Effective interventions have lessened the severity of children's language and intellectual delays, experts say.17 In addition, doctors have been diagnosing children with ASD at younger ages, so treatment and therapies often begin earlier.17 In fact, in 2012, researchers reported that toddlers who underwent an autism therapy called the Early Start Denver Model showed improvements in intelligence, as well as language.18 Other effective therapies include intensive early interventions that use the principles of Applied Behavior Analysis.

Researchers hope to develop a better understanding of how autism affects the brain. Many have looked at the unusual patterns of strengths and weaknesses in people with autism. Although people with autism vary greatly, many have relatively better visual processing abilities than verbal (language) abilities.5 For example, a person's visual and spatial reasoning skills would enable him to imagine how objects look from different angles and fit together. On an individual level, knowing that a particular child has stronger visual skills may influence how his parents and teachers help him learn. He may respond better to picture schedules than to spoken instructions, for example. A neuropsychological assessment, which may include measures of intelligence, adaptive skills, behavior, attention and social-emotional skills, may provide a fuller picture of the person's strengths and weaknesses, potentially for use by therapists and teachers.

Several prominent autism researchers set out to define the "cognitive phenotype" – essentially the intellectual profile – of autism several years ago. They found the task challenging, noting that as yet no one has found a distinct pattern that distinguishes "high vs. low IQ individuals with ASD."16 Their study, described as preliminary, concluded with a call for more research on intellectual profiles. These profiles could help guide future interventions as well as provide "a window into the 'autistic experience.'"16

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Additional Resources: 
  1. Interactive Autism Network (2007, August 1). IAN Research Report #2 – July 2007. View.
  2. American Psychiatric Association. (2013). Diagnostic and statistical manual of mental disorders (5th ed.). Arlington, VA: American Psychiatric Publishing.
  3. Gould, S.J. (1996) The mismeasure of man. New York: W. W. Norton & Company.
  4. Duncan, A.W. & Bishop, S.L. (2015) Understanding the gap between cognitive abilities and daily living skills in adolescents with autism spectrum disorders with average intelligence. Autism, 19(1):64-72. Abstract.
  5. Tsatsanis, K. D. & Powell, K. (2014). Neuropsychological Characteristics of Autism Spectrum Disorders. In F. R. Volkmar et al. (Eds.), Handbook of Autism and Pervasive Developmental Disorders (4th ed.) Hoboken, NJ: John Wiley & Sons. pp. 302-331.
  6. Gerhardt, P.F. (2014) Autism, Adulthood and Adaptive Behavior. Online Presentation for the Simons Simplex Community@Interactive Autism Network. View.
  7. Thioux, M., Stark, D.E., Klaiman, C., & Schultz, R.T. (2006) The day of the week when you were born in 700 ms: Calendar computation in an autistic savant. Journal of Experimental Psychology: Human Perception and Performance, 32(5), 1155-1168. Abstract.
  8. Stanutz, S., Wapnick, J. & Burack, J. A. (2014) Pitch discrimination and melodic memory in children with autism spectrum disorders. Autism, 18(2), 137-147. Abstract.
  9. Eigsti, I-M. & Fein, D.A. (2013) More is less: Pitch discrimination and language delays in children with optimal outcomes from autism. Autism Research, 6, 605-613. Abstract.
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  11. Bonnel, A., McAdams, S., Smith, B., Berthiaume, C., Bertone, A., Ciocca, V., Burack, J.A. & Mottron, L. (2010) Enhanced pure-tone pitch discrimination among persons with autism but not Asperger syndrome. Neuropsychologia, 48, 2465-2475. Abstract.
  12. Heaton, P., Hudry, K., Ludlow, A. & Hill, E. (2008) Superior discrimination of speech pitch and its relationship to verbal ability in autism spectrum disorders. Cognitive Neuropsychology, 25(6), 771-782. Abstract.
  13. Mayer, J.L., Hannent, I., & Heaton, P.F. (2014) Mapping the developmental trajectory and correlates of enhanced pitch perception on speech processing in adults with ASD. Journal of Autism and Developmental Disorders. DOI: 10.1007/s10803-014-2207-6. Abstract.
  14. Fombonne, E. (1999) The epidemiology of autism: a review. Psychological Medicine, 29(4):769-86. Abstract.
  15. Autism and Developmental Disabilities Monitoring Network Surveillance Year 2010 Principal Investigators. (2010). Prevalence of Autism Spectrum Disorder Among Children Aged 8 Years – Autism and Developmental Disabilities Monitoring Network, 11 Sites, United States, 2010. Retrieved from
  16. Charman, T., Jones, C.R.G., Pickles, A., Simonoff, E., Baird, G. & Happe, F. (2011) Defining the cognitive phenotype of autism. Brain Research, 1380, 10-21. Abstract.
  17. Rogers, S. J. & Vismara, L. Interventions for Infants and Toddlers at Risk for Autism Spectrum Disorder In F. R. Volkmar et al. (Eds.), Handbook of Autism and Pervasive Developmental Disorders (4th ed.) Hoboken, NJ: John Wiley & Sons. pp. 739-769.
  18. Dawson, G., Jones, E.J., Merkle, K., Venema, K., Lowy, R., Faja, S. Kamara, D., Murias, M., Greenson, J., Winter, J., Smith, M., Roger, S.J. & Webb, S.J. (2012) Early behavioral intervention is associated with normalized brain activity in young children with autism. Journal of the American Academy of Child and Adolescent Psychiatry, 51(11):1150-9. Abstract