Cognitive Assessment, Research Link

No, the WISC-IV doesn’t underestimate the intelligence of children with autism.

The title of a new study asks “Does WISC-IV underestimate the intelligence of autistic children?” The authors’ answer is that it probably does. I believe that the reasoning behind this conclusion is faulty.

This study gives the unwarranted impression that it is a disservice to children with autism to use the WISC-IV. Let me be clear—I want to be helpful to children with autism. I certainly do not wish to do anything that hurts anyone. A naive reading of this article leads us to believe that there is an easy way to avoid causing harm (i.e., use the Raven’s Progressive Matrices test instead of the WISC-IV). In my opinion, acting on this advice does no favors to children with autism and may even result in harm.

Based on the evidence presented in the study, the average score differences between children with and without autism is smaller on Raven’s Progressive Matrices (RPM) and larger on the WISC-IV. The rhetoric of the introduction leaves the reader with the impression that the RPM is a better test of intelligence than the WISC-IV. Once we accept this, it is easy to discount the results of the WISC-IV and focus primarily on the RPM.

There is a seductive undercurrent to the argument: If you advocate for children with autism, don’t you want to show that they are more intelligent rather than less intelligent? Yes, of course! Doesn’t it seem harmful to give a test that will show that children with autism are less intelligent? It certainly seems so!

Such rhetoric reveals a fundamental misunderstanding of what individual intelligence tests like the WISC-IV are designed to do. In the vast majority of settings, they are not for certifying how intelligent a person is (whatever that means!). Their primary purpose is to help psychologists understand what a person can and cannot do. They are designed to help explain what is easy and what is difficult for a person so that appropriate interventions can be selected.

The WISC-IV provides a Full Scale IQ, which gives an overall summary of cognitive functions. However, it also gives more detailed information about various aspects of ability. Here is a graph I constructed from Figure 1 in the paper. In my graph, I converted percentiles to index scores and rearranged the order of the scores to facilitate interpretation.


Average Raven’s Progressive Matrices (RPM) and WISC-IV scores for children with and without autism

It is clear that the difference between the two groups of children is small for the RPM. It is also clear that the difference is also small for the WISC-IV Perceptual Reasoning Index (PRI). Why is this? The RPM and the PRI are both nonverbal measures of logical reasoning (AKA fluid intelligence). Both the WISC-IV and the RPM tell us that, on average, children with autism perform relatively well in this domain. The RPM is a great test, but it has no more to tell us. In contrast, the WISC-IV not only tells us what children with autism, on average, do relatively well, but also what they typically have difficulty with.

It is no surprise that the largest difference is in the Verbal Comprehension Index (VCI), a measure of verbal knowledge and language comprehension. Communication problems are a major component of the definition of autism. If children with autism had performed equally well on the VCI, we would wonder whether the VCI was really measuring what it was supposed to measure. Note that I am not saying that a low score on VCI is a requirement for the diagnosis of autism or that the VCI is the best measure of the kinds of language problems that are characteristic of autism. Rather, I am saying that children with autism, on average, have difficulties with language comprehension and that this difference is manifest to some degree in the WISC-IV scores.

The WISC-IV scores also suggest that, on average, children with autism not only have lower scores in verbal knowledge and comprehension, they are more likely to have other cognitive deficits, including in verbal working memory (as measured by the WMI) and information processing speed (as measured by the PSI).

Thus, as a clinical instrument, the WISC-IV performs its purpose reasonably well. Compared to the RPM, it gives a more complete picture of the kinds of cognitive strengths and weaknesses that are common in children with autism.

If the researchers wish to demonstrate that the WISC-IV truly underestimates the intelligence of children with autism, they would need to show that it underpredicts important life outcomes among this population. For example, suppose we compare children with and without autism who score similarly low on the WISC-IV. If the WISC-IV underestimated the intelligence of children with autism, they would be expected to do better in school than the low-scoring children without autism. Obviously, a sophisticated analysis of this matter would involve a more complex research design, but in principle this is the kind of result that would be needed to show that the WISC-IV is a poor measure of cognitive abilities for children with autism.


6 thoughts on “No, the WISC-IV doesn’t underestimate the intelligence of children with autism.

  1. concerned parent says:

    Mr. Schneider – I read you article and I’m not a psychologist just an interested parent looking for information about testing for my child. How would you account for average scores on the WISC and superior academic scores for a child with mild autism?

    • Good question.
      There are lots of possible reasons for this:
      1. Measurement error in either the WISC or the academic scores.
      2. A child who is working really hard in school.
      3. A parent who is working really hard to help the child in school.
      4. A really fantastic school.
      and many, many others.

  2. Shawn says:

    I’m not real convinced by your analysis here. You assert people with autism “are more likely to have other cognitive deficits”. Simply because on average autistics have lower scores in working memory for example doesn’t make it a better test.

    I guess what you are asserting is that Raven doesn’t capture working memory and the WISC-IV does.

    I believe your assertation to be demonstrably false and evidenced in the literature … there is a “typically strong correlation between measures of WMC and overall performance on Raven”

    So if Raven scores are higher and that reflects working memory, then why does WISC-IV

  3. Interesting article, but I fear that in doesn’t speak to the main problem of that gap, nor acknowledge the proven power of RPM. As you concentrate on, WISC-IV is still a better test of where a child is now, but RPM remains the supreme test of where they could be. This is why I find the gap between RPM and *all* WISC-IV subtests troubling, and any diminution of that problem a worry – as it should otherwise be a Clarion call for research in to radical new teaching strategies.

  4. Justin Digney says:

    Thanks Joel,

    I came across your article after reading a paper that convincingly demonstrated that the RPM does better illustrate the strengths of Autism/Aspergers. Of course that was the purpose of the research, to show Autism Spectrum Disorder does not necessarily have a lower IQ but rather a different IQ.

    While originally highly skeptical of your article it is clear that you are correct. From an “employability” perspective, the RPM over estimates an employees Overall skills.

    However the summation process of General IQ is highly flawed in this regard. For example my Spacial skills IQ (assessed at age 6) was 130, and my general IQ was 120. My high spacial skills along with other strengths ‘clearly’ significantly skewed my overall IQ results.

    From a social interaction point of view the summation process to form a general IQ result does ASD a total disjustice. Indeed, looking at the Quality of Life (QoL) findings for Adults on the spectrum, and government policies, (particularly here in Australia), Higher general IQ is strongly correlates with low QoL.

    I don’t know if an IQ test for social awkwardness exists. I know from my own observation that my inference (as related to literacy) skills are significantly atypical. Autism appears to focus around fundamental ‘use’ of language. Written, verbal and non-verbal language (facial expression, body language, tone, volume).

    The impairment of having atypical language skills is SIGNIFICANTLY underplayed in public policy around the management/support afforded to Autism.

    In QoL terms ASD outcomes worsen with increased general IQ, yet support is non-existent. While it is the expectation of general society for ASD (and all individuals) to conform to social expectations, ASD appears to draw its social expectations via alternative means (I am not sure if this has even been researched), reflecting societies mantras and ideals as opposed to its realities.

    For Psychology to do service to ASD it must find a way to highlight the ‘very’ real disadvantage atypical IQ (or specific/related peak IQ) has on adult function in the contemporary workplace.

    I have no doubt (zero) that general IQ is a relevant measure in its current form. The issue relates 100% to social expectations. The broader public expect people with a given level of intelligence to have a typical IQ distribution (form of standard deviation if you like). Individuals with an atypical ‘standard deviation’ are impaired demonstrably.

    Infact, the relatively low nuanced the understanding of General IQ (by the general public), that general IQ could/should be reported differently. Without knowing anything of the calculation of General IQ, I proposed to report the highest IQ, and the difference between the highest and the lowest, therefore IQ could/should be reported as 100/30 (ie lowest facit 100, highest 130). Clearly for Neuro-Typical this would be expected to be something in the order of (100/5).

    This cleary has more value if we can accurately measure an individual’s Emotional Intelligence (EQ) and incorporate this into the general IQ score. Alternativley an accurate measure of EQ to be used for disability support funding? I am not aware of research being done into the relationship between EQ/IQ and QoL. I speculate EQ=IQ has a correlation with IQ/QoL. Whereas IQ>EQ has a correlation with low QoL, and EQ>IQ has a correlation with high QoL.

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