I am so excited about tonight’s article about autism and the Wechsler intelligence scales that I practically ran home from work to write it.
There are a lot of Wechsler people who read this blog. A lot of Wechsler examiners and a lot of Wechsler examinees.
At the same time I’m proud to say I have a HUGE autistic readership and also have a growing readership of autism moms (and dad’s, but I only care about mom’s because women get it in a way that most men don’t; besides we have too many guys here).
Anyways, do I have a treat for all of you: The Wechsler Autism Index (WAI).
The great David Wechsler (author of the Wechsler intelligence scales) would have been like a kid in a candy store had he lived long enough to see the popularization of autism, but in his day autism was barely recognized as a condition, and when it was, it was often classified as childhood schizophrenia.
Since Wechsler didn’t live long enough to create the Wechsler Autism Index, I decided to do it for him. I began by researching whether autistics had a certain profile of strengths and weaknesses on the Wechsler scales and found a paper that summarized the research:
In autism, on the Verbal Comprehension Tests the Comprehension subtest is typically substantially lower than Information, Vocabulary and Similarities. On the Perceptual Organization subtests, Block Design is substantially higher than Picture Completion and Picture Arrangement. Digit Symbol may also be depressed.
It makes sense that autistics would perform relatively poorly on the Comprehension subtest because Wechsler originally conceived this is as a measure of common sense social understanding. I was recently amused when a commenter suggested it was autistic to support affirmative action, when “Why is affirmative action needed?” is exactly the type of question you’d find on the Comprehension test on which autistics do worst, but it also shows how ideological the Comprehension subtest can be.
In his book A Question of Intelligence, the late great Fortune magazine editor Daniel Seligman described taking the Wechsler Comprehension subtest:
Next [examiner] Stern brought on a subtest that, I later learned, is called Comprehension. It gauges your ability to organize information about the world you live in and arrive at some common sense understanding of various social phenomena. Most of the questions seemed sensible, but I found myself suddenly rebelling against one question on ideological grounds. The question assumed a need for certain laws bearing on labor relations and asked why they were needed. My instant answer, which would have been backed by many eminent economists, was that the laws are not needed and are in fact counterproductive. Obviously uninterested in debating social policy, Stern cheerfully restated the question so that all you needed to produce was the theory behind the laws. I got scored correct for the theory (and generally did quite well on Comprehension); however, I found myself still muttering about David Wechsler’s grasp of economics.
There’s a stereotype that libertarians and economists are a bit autistic or aspergoid (conditions where Theory of Mind is impaired, so they can’t understand how other people think). Libertarians are criticized for not understanding how society, business and incentives really work and economists are criticized for assuming people behave rationally. Indeed there’s a whole movement called post-autistic economics.
These criticisms could be nonsense, but I find it absolutely fascinating that the Comprehension subtest, which was created long before people talked about autism or Asperger’s, yet has historically been thought to measure social intelligence, included an item that libertarians and eminent economists would object to.
It also makes sense that autistics would score relatively poorly on Picture Arrangement because this test requires you to arrange a series of cartoon pictures into the correct order to tell a sensible story and this sometimes requires an ability to interpret social situations, get the joke, and see the big picture. Perhaps autistics sometimes struggle to see the big picture because they are sometimes said to be better at seeing specific details because of too much local (short-range) brain processing and the expense of global (long-range) processing.
I’m not surprised to learn autistics do relatively poorly on the Digit-Symbol subtest (sometimes called Coding). This test requires hand-eye coordination and rapid attention switching (two abilities autistics are relatively poor on), but it also seems biased against people who have an obsessively conscientious personality (as many autistics do) because if you’re too concerned about accuracy, your speed on this test will suffer.
On the other hand I was surprised to learn that autistics do poorly on Picture Completion, a test where you need the visual alertness to see what’s missing from a picture of a common object or scene. In fact I would have thought autistics would do well on this test given their attention to detail, but sometimes people score low because they see something trivial missing from the picture, instead of the feature the test maker intended them to see. For example on the Picture Completion item from the Army Beta IQ test used in WWI, perhaps an autistic would say the body is missing, which while technically true, is not what was intended.
Perhaps having an intuitive understanding of what the test designer intended to be missing requires “Theory of Mind”; largely the ability to understand the intentions of others. Impaired Theory of Mind is a key deficit in autism. Or it could simply be that autistics struggle with this test because poor visual alertness causes one to miss social cues and dress inappropriately, and thus makes one more likely to be diagnosed as autistic whether they have it or not (assuming it has an objective existence).
On the flip-side autistics do relatively well on Information (general knowledge), Vocabulary (word knowledge), Similarities (verbal abstraction), and Block Design (spatial analysis).
The Wechsler autism index
Armed with this profile, I created the Wechsler autism index which is simply the ratio of one’s scores on the subtests that autistics do relatively well on to the subtest they do relatively poorly on:
Wechsler Autism Index = (Information scaled score + Vocabulary scaled score + Similarities scaled score + 3*Block Design score)/( Picture Arrangement scaled score + Picture Completion scaled score + Digit Symbol score + 3*Comprehension score)
The higher the index, the more autistic one is likely to be, but no psychologist should ever use this index as the sole criterion in diagnosing autism, it is simply one data point to consider.
I wanted to make sure verbal and non-verbal subtests were given equal weight so since there were three verbal subtests autistics do relatively well on and only one non-verbal subtest (Block Design) they do relatively well on, I multiply the Block Design score by 3 so that non-verbal autistic strengths get the same weight as verbal autistic strengths.
Similarly, since there was only one verbal subtest that autistics do relatively poorly on (Comprehension), but three non-verbal subtests they struggle with , I gave the verbal subtest three times as much weight.
I did this because there’s no consistent evidence that autistic have a higher verbal than non-verbal IQ, so I didn’t want the formula to imply high verbal IQ types are more autistic than high non-verbal IQ types.
Sadly, the Picture Arrangement subtest has been dropped from the latest revision of the WAIS, so for those taking the WAIS-IV, the autism index could be calculated as follows:
Wechsler Autism Index = (Information scaled score + Vocabulary scaled score + Similarities scaled score + 3*Block Design score)/( 1.5*Picture Completion scaled score + 1.5*Digit Symbol score + 3*Comprehension score)
Picture Completion and Digit Symbol are multiplied by 1.5 to makeup for Picture Arrangement missing.