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.
Autism Prevalence
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).
The intelligence levels of autistic people, in general, are highly polarized, with many autistic people scoring average to above-average; compared to the general public, more autistic people score in the gifted range (140+ IQ).
Autistic Individuals Require Specialized IQ Tests
It's not surprising that IQ testing for individuals with ASD is even more complex and controversial. Since verbal skills deficits are one of the key symptoms of autism, IQ testing that relies heavily on those skills for the assessment normally falls flat.
However, epidemiological data from different countries indicate a high prevalence of low intelligence quotient (IQ) scores in children with ASD. According to the most recent ASD surveillance estimates in the US, 35% of 8‐year‐old children with ASD have Intellectual Disability (ID) (IQ < 70, Maenner et al., 2021).
For instance, among the 18 studies under scrutiny that did not explicitly state an IQ cut-off point the mean range of IQ among individuals with ADHD reported in the studies is from 102 to 110. Given that lower IQ is associated with ADHD this suggests that individuals with ADHD may be inaccurately represented.
Those with Asperger's syndrome, in contrast, must by definition have suffered no cognitive delay during their first 3 years of life. This means that they will usually have at least a “normal” IQ. In some cases, their IQ may be very high, even in the genius range. There are, however, different kinds of smarts.
There are several kinds of IQ tests available, but standard IQ tests usually given to children with autism are the Verbal Intelligence Quotient (VIQ) test, Performance Intelligence Quotient (PIQ) test, or the Full-Scale Intelligence Quotient (FSIQ) test.
Someone who is considered a savant may be especially skilled in art, math, music, memory recall, or another subject. Savant syndrome is commonly associated with autism but can occur alongside other conditions.
About 70% of autistic people have an intellectual disability, which means they have an IQ lower than 70. The remaining 30% have intelligence that ranges from average to gifted. Autism and intelligence are two separate characteristics. A person can be autistic with any level of intelligence.
However, the fitness tests showed that aerobic fitness, flexibility and body mass index of children with autism spectrum disorders was similar to the children without autism. The strength test was the only one that children with autism spectrum disorders did not perform as well in, the study said.
Research shows that more than half of all autistic individuals have an above-average IQ, while roughly 16% have an IQ higher than 130. But having high intelligence doesn't mean that autistic individuals don't experience some challenges associated with the diagnosis.
However, there is no correlation between this condition and intelligence. In fact, according to one study , ADHD affects people in the same way across high, average, and low IQ score ranges. ADHD is a neurodevelopmental condition that can make it difficult for people to focus and to control impulsive behaviors.
The impact of ADHD on IQ
Even though ADHD and high IQ do coexist, ADHD symptoms can interfere with IQ testing. A 2015 study of 4,771 pairs of twins demonstrated the connection between ADHD symptoms and lower IQ scores. ADHD can also interfere with individual areas of performance, such as executive functioning.
The measured IQ for persons with mild ID is between 50–55 and 70 (based on population mean of 100; 1 standard deviation of 15, and margin of measurement error of ±5) (8,10,13-16).
IQ test results fall along the normal (bell-shaped) curve, with an average IQ of 100, and individuals who are intellectually disabled are usually two standard deviations below the average (IQ below 70).
Persons with a mild intellectual disability (MID; intelligence quotient (IQ) range 50–69) or borderline intellectual functioning (BIF; IQ range 70–85) are vulnerable for problems in different domains.
Not All Autistics Are Mathematic Savants, But Many Have Above-Average Math Abilities. It turns out that, despite impressions, most ASD patients may not be any better at math than their counterparts at a particular age or developmental stage.
It is a myth that all autistic people have an intellectual disability. The truth is that 2/3 of people on the spectrum have average or above-average IQs.
Therefore, it appears that while some individuals may be aware they are autistic, others may not fully understand why they have difficulties connecting with people socially or engaging in conversation - yet still realize they are 'different.
But genetics can explain the wide range of possible IQs too because so many different genes are involved in developing and running a brain. It is possible, for example, to inherit all the higher IQ genes from each parent and leave the lower IQ ones behind. Now the child will be brighter than the parent.
ADHD AND GIFTEDNESS are sometimes described as having the same or similar characteristics. However, one diagnosis is considered a disability and one, a gift. Neither assumption is ideal in supporting the child identified with either ADHD, giftedness, or both, often referred to as twice exceptional or 2e.