Autism and iq

Measuring Intelligence in Autism | Kennedy Krieger Institute

Marina Sarris
Interactive Autism Network at Kennedy Krieger Institute

[email protected]

Date Published: October 20, 2015

Intelligence 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.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?

When 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," 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

From 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

Additional Resources: 

  • What does research say about early interventions for autism? See IAN's Therapies and Treatments for Autism.


  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.
  10. Jones, C.R.G., Happe, F., Baird, G., Simonoff, E., Marsden, A.J.S., Tregay, J., Phillips, R. J., Goswami, U., Thomson, J. M. & Charman, T. (2009) Auditory discrimination and auditory sensory behaviours in autism. Neuropsychologia, 47, 2850-2858. Abstract.
  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

Autism Statistics and Facts | Autism Speaks

Autism Prevalence

  • In 2021, the CDC reported that approximately 1 in 44 children in the U.S. is diagnosed with an autism spectrum disorder (ASD), according to 2018 data.
    • 1 in 27 boys identified with autism
    • 1 in 116 girls identified with autism
  • Boys are four times more likely to be diagnosed with autism than girls.
  • Most children were still being diagnosed after age 4, though autism can be reliably diagnosed as early as age 2.
  • 31% of children with ASD have an intellectual disability (intelligence quotient [IQ] <70), 25% are in the borderline range (IQ 71–85), and 44% have IQ scores in the average to above average range (i.e., IQ >85).
  • Autism affects all ethnic and socioeconomic groups.
  • Minority groups tend to be diagnosed later and less often.
  • Early intervention affords the best opportunity to support healthy development and deliver benefits across the lifespan.
  • There is no medical detection for autism.

What causes autism?

  • Research indicates that genetics are involved in the vast majority of cases. 
  • Children born to older parents are at a higher risk for having autism. 
  • Parents who have a child with ASD have a 2 to 18 percent chance of having a second child who is also affected. 
  • Studies have shown that among identical twins, if one child has autism, the other will be affected about 36 to 95 percent of the time. In non-identical twins, if one child has autism, then the other is affected about 31 percent of the time.  
  • Over the last two decades, extensive research has asked whether there is any link between childhood vaccinations and autism. The results of this research are clear: Vaccines do not cause autism. 

Intervention and Supports 

  • Early intervention can improve learning, communication and social skills, as well as underlying brain development.   
  • Applied behavior analysis (ABA) and therapies based on its principles are the most researched and commonly used behavioral interventions for autism. 
  • Many children affected by autism also benefit from other interventions such as speech and occupational therapy. 
  • Developmental regression, or loss of skills, such as language and social interests, affects around 1 in 5 children who will go on to be diagnosed with autism and typically occurs between ages 1 and 3. 

Associated Challenges 

  • An estimated 40 percent of people with autism are nonverbal.  
  • 31% of children with ASD have an intellectual disability (intelligence quotient [IQ] <70) with significant challenges in daily function, 25% are in the borderline range (IQ 71–85). 
  • Nearly half of those with autism wander or bolt from safety.  
  • Nearly two-thirds of children with autism between the ages of 6 and 15 have been bullied. 
  • Nearly 28 percent of 8-year-olds with ASD have self-injurious behaviors. Head banging, arm biting and skin scratching are among the most common. 
  • Drowning remains a leading cause of death for children with autism and accounts for approximately 90 percent of deaths associated with wandering or bolting by those age 14 and younger. 

Associated Medical & Mental Health Conditions 

  • Autism can affect the whole body. 
  • Attention Deficient Hyperactivity Disorder (ADHD) affects an estimated 30 to 61 percent of children with autism. 
  • More than half of children with autism have one or more chronic sleep problems. 
  • Anxiety disorders affect an estimated 11 to 40 percent of children and teens on the autism spectrum. 
  • Depression affects an estimated 7% of children and 26% of adults with autism. 
  • Children with autism are nearly eight times more likely to suffer from one or more chronic gastrointestinal disorders than are other children. 
  • As many as one-third of people with autism have epilepsy (seizure disorder).  
  • Studies suggest that schizophrenia affects between 4 and 35 percent of adults with autism. By contrast, schizophrenia affects an estimated 1.1 percent of the general population. 
  • Autism-associated health problems extend across the life span – from young children to senior citizens. Nearly a third (32 percent) of 2 to 5 year olds with autism are overweight and 16 percent are obese. By contrast, less than a quarter (23 percent) of 2 to 5 year olds in the general population are overweight and only 10 percent are medically obese. 
  • Risperidone and aripiprazole, the only FDA-approved medications for autism-associated agitation and irritability. 

Caregivers & Families  

  • On average, autism costs an estimated $60,000 a year through childhood, with the bulk of the costs in special services and lost wages related to increased demands on one or both parents. Costs increase with the occurrence of intellectual disability. 
  • Mothers of children with ASD, who tend to serve as the child’s case manager and advocate, are less likely to work outside the home. On average, they work fewer hours per week and earn 56 percent less than mothers of children with no health limitations and 35 percent less than mothers of children with other disabilities or disorders. 

Autism In Adulthood  

  • Over the next decade, an estimated 707,000 to 1,116,000 teens (70,700 to 111,600 each year) will enter adulthood and age out of school based autism services. 
  • Teens with autism receive healthcare transition services half as often as those with other special healthcare needs. Young people whose autism is coupled with associated medical problems are even less likely to receive transition support. 
  • Many young adults with autism do not receive any healthcare for years after they stop seeing a pediatrician. 
  • More than half of young adults with autism remain unemployed and unenrolled in higher education in the two years after high school. This is a lower rate than that of young adults in other disability categories, including learning disabilities, intellectual disability or speech-language impairment.  
  • Of the nearly 18,000 people with autism who used state-funded vocational rehabilitation programs in 2014, only 60 percent left the program with a job. Of these, 80 percent worked part-time at a median weekly rate of $160, putting them well below the poverty level. 
  • Nearly half of 25-year-olds with autism have never held a paying job. 
  • Research demonstrates that job activities that encourage independence reduce autism symptoms and increase daily living skills. 

Economic Costs 

  • The cost of caring for Americans with autism had reached $268 billion in 2015 and would rise to $461 billion by 2025 in the absence of more-effective interventions and support across the life span. 
  • The majority of autism’s costs in the U.S. are for adult services – an estimated $175 to $196 billion a year, compared to $61 to $66 billion a year for children. 
  • On average, medical expenditures for children and adolescents with ASD were 4.1 to 6. 2 times greater than for those without autism.   
  • Passage of the 2014 Achieving a Better Life Experience (ABLE) Act allows tax-preferred savings accounts for people with disabilities, including autism, to be established by states.  
  • Passage of autism insurance legislation in all 50 states is providing access to medical treatment and therapies. 

For more information, download Autism and Health: A Special Report by Autism Speaks. 


The study showed that IQ increases were greatest in those people who had a loss of language skills (regression) in early childhood, and who had more communication problems at the age of 12 years. Among people with autism who regressed, IQ increased by an average of 15.4 points, compared with 6.6 points among those who did not regress.

In contrast to the rise in IQ, the overall trajectory of autism symptoms reported by parents, although highly variable among individuals, remained on average unchanged over this period. nine0003

At the same time, studying in a general education class or studying in any type of specialized class was not associated with an increase in IQ. However, in those children who studied in general education classes, autism symptoms were much more likely to decrease by adulthood.

“We worked with this unique sample of autistic children to better understand their development and perspectives as adults,” says Emily Simonoff, Professor of Child and Adolescent Psychiatry at King's College London. “Our current understanding of prognosis for autistic children in adulthood is still largely based on clinical samples that include only the most severe cases of autism.” nine0003

This study included children from the Special Needs and Autism UK Project, a cohort study in the general population that began in 2000 to assess the prevalence of autism. The original sample was over 56,000 children aged 9-10 who lived in southeast England. The sample also included children with special educational needs for any reason or with a clinical diagnosis of autism.

By age 12, only 158 children in this sample had received an official diagnosis of autism. The authors of the study tested these children at the age of 12, 16 and 23 years. IQ test scores and the severity of autistic traits were major indicators of whether autistic young people would be able to function independently in daily life. nine0003

The strength of the study was that the same instruments were used at each age interval, and then their results were easy to interpret. The researchers also used a statistical approach to identify factors influencing IQ levels and autistic traits, as well as factors that indicated changes in the future.

Variation in IQ levels among study participants was similar to that commonly observed among autistic children, ranging from severe intellectual impairment (IQ 120). nine0003

There is a standardized IQ test for every age, so it usually doesn't change as you get older. This means that if the IQ level increased by 7.48 points, this indicates really significant changes in intellectual abilities that are noticeable to parents and teachers.

“Part of these changes can be explained by an increase in social motivation or the very ability to test, rather than a change in the ability to learn as such. These alternative explanations are also important aspects of real-life functioning and may open up new educational and employment opportunities for autistic people,” adds Dr. Simonoff. Poor language skills and greater severity of autism at age 12 predicted overall IQ (but not changes in IQ). nine0003

This study shows for the first time that language regression in early childhood is associated with the developmental trajectory of intelligence. An earlier study in the same cohort found that children who experienced regression in language skills had more advanced cognitive development in early childhood compared to the rest of the sample. One of the possible explanations for this phenomenon is that regression is associated with a certain type of development in which the cognitive sphere can return to its original trajectory. nine0003

With regard to the severity of autistic traits in adolescence and adulthood, they were primarily associated with autistic symptoms in early childhood and the presence of comorbid mental health problems.

Other important data from the study is that children who were taught in general education classes had fewer symptoms of autism during adolescence and adulthood than those who studied in any of the specialized classes. Potentially, this data can have important implications for educational decision making. nine0003

“Our statistical approach tried to take into account the influence of other factors - after all, it is clear that children are offered this or that type of education for a reason. We cannot exclude that some unaccounted for factors explain this result. However, these data suggest that the inclusive education of autistic children contributes to their social development,” concludes Dr. Simonoff.

Education in a general education environment requires the creation of special educational conditions for autistic children, and education in a general education class is not available for all children. Further identification of which components can improve this access could also improve the developmental trajectory in autism for more children. nine0003

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Autism without intellectual disability is more common than previously thought • Autism is

More than half of autistic people in the United States have an average or above average intelligence quotient (IQ), a significant increase over previous estimates. This is stated in the results of a new longitudinal study conducted among children in the US state of Minnesota. nine0003

The increase in autism without intellectual disability may reflect increased awareness and knowledge about autism, as well as improvements in detection and diagnosis tools and procedures, said study lead author Maja Katusic, a pediatrician at the Mayo Clinic in Rochester, Minnesota.

In 2016, the proportion of autistic children in the United States with an average or higher IQ was 42%, according to the prevalence of autism published by the US Centers for Disease Control and Prevention (CDC) in 2020. nine0003

However, this share is 59% according to a new study.

Katusik and her colleagues analyzed the medical and school records of more than 30,000 people born between 1976 and 2000 in Olmsted County, Minnesota. They identified people with autism based on behavioral testing and descriptions using the broad or narrow definition of autism from the Diagnostic and Statistical Manual of Mental Disorders, fourth edition (DSM-IV). The broad definition included children who met the criteria for autistic disorder, Asperger's syndrome, or pervasive developmental disorder not specified, while the narrow definition covered only autistic disorder. Researchers also noted officially diagnosed autism documented in records. nine0003

Of the 890 people whose records contained IQ testing data and who met the extended definition of autism, 59% had an IQ score of average or above average, 86 or higher. Among the 453 people who fit the narrow definition, this was true for 51%.

At the same time, 187 people with IQ data were officially diagnosed with autism, and among them only 43% did not have intellectual disabilities. The results of the study were published in the November issue of the scientific journal Pediatrics. nine0003

The results suggest that it is easier for clinicians to identify cases of autism with below-average IQs. At the same time, people with higher IQs may not receive the correct diagnosis, as a result of which they are deprived of access to services that could help them.

"Autistic people with an average or higher IQ may still have difficulty with relationships, employment, and daily activities," says Katusik.

The proportion of boys without intellectual disability was higher than the proportion of girls among all three diagnoses (autistic disorder, Asperger's syndrome, pervasive developmental disorder, unspecified). According to Katusik, autistic girls are on average diagnosed later than boys and may hide autistic traits.

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