Unfortunately, there is a great deal of confusion, and therefore misunderstanding, around what is meant by “high-functioning” and “low-functioning” autism.
The commonsense use of the word “functioning” has to do with, well, functioning. Most people would probably associate “functioning” with the usual meaning of “to work or operate, to carry on a function.”
But in the academic/scientific autism world, there is only a loose connection between the vernacular sense of the word and the label.
And my impression is that the clinical world is somewhere between these two, adding yet more confusion. A few years ago, for example, there was a raging debate about whether there is a difference between “high-functioning autism” and “Asperger syndrome.” The only pragmatic difference I could detect in who got which label was whether there was a delay in the acquisition of spoken language (“high-functioning”) or no delay (“Asperger’s”).
In the psychology community, the phrase used to describe the commonsense meaning of “functioning” is “adaptive behavior.” There is a related term, “functional behavior,” but that seems to be more about understanding the purpose (or function) of maladaptive behaviors.
Adaptive behavior reflects an individual’s social and practical competence of daily skills to meet the demands of everyday living. Behaviors change throughout development, across life settings and cultures, and through social constructs and expectations of others. It is important to assess adaptive behavior in addition to IQ in order to determine how well an individual functions in daily life.
Part of the problem here is that autism and true adaptive behavior skills have very little to do with each other. Celine Saulnier of Emory University spoke at a conference I attended a couple of years ago and emphatically stated that “functioning means IQ, and that’s all it means!” when describing autism.
She pointed out that not many years ago, it was thought that autism and intellectual impairment where highly correlated, with perhaps 70% to 80% of autistic people being cognitively impaired (generally defined as having an IQ not above 70). Today, the common wisdom seems to be the other way around, but Dr. Saulnier’s work (citations at her PubMed page) and that of others has shown that there is effectively no correlation between IQ and measures of autism such as the ADOS scale.
The mention of this diagnostic scale risks opening another can of worms, that of “severity” in autism. That is best left for another post, so let me just mention in passing that my interpretation of the ADOS (and other such scales) is that they measure how easy or difficult it is to tell from behavioral observation whether someone is autistic. A person who exhibits more obvious autistic behaviors is not necessarily “more” autistic than someone who has fewer outward signs.
There is another concept relating to the definition of adaptive behavior given earlier, and many commercial products exist that quantify this functional adaptive behavior. The best-known of these is perhaps the Vineland Scale, but there are several others that are in use. Dr. Saulnier observed that there is also no correlation between ADOS scores and Vineland scores, meaning that the “degree” of autism that is observed in a person says nothing about that person’s ability to function in life.
What, then, does it mean to label someone as a “low-functioning” autistic? Simply put, it is an autistic person who is cognitively impaired. This, as mentioned, is generally defined as having an IQ of no more than 70. There is more than one IQ scale, and different ways of standardizing test scores, but overlooking that wrinkle, the reason 70 was chosen is that it is two standard deviations below the mean IQ of 100. In keeping with the findings of Professor Saulnier and others, suggesting that the prevalence of cognitive impairment is the same in the autistic population as it is in the general population, or 2.28%. It follows that nearly 98% of autistic people are “high-functioning.”
As an aside, the federal statute known as the DD Act contains a definition of developmental disability (both cognitive impairment and autism are considered to be developmental disabilities). There is no IQ test in that definition; it is all about a disability that
results in substantial functional limitations in 3 or more … areas of major life activity
Given the significant limitations that IQ tests have in predicting success in such “areas of major life activity” I asked around to see if the general understanding of “low-functioning autism” really did include that arbitrary cutoff. Yes, I was told over and over again from researchers I know and respect. Even if not stated, it was understood that 70 was the cutoff, although some studies explicitly used other breakpoints, such as 80.
Most studies define high-functioning children as those with an IQ above 70 or 80, but this is problematic for a number of reasons, say some scientists.
Although this article has a different take on what percentage of autistic people are cognitively impaired, it does confirm what my informal contacts had been telling me.
In addition, it points out many problems with associating IQ-type intelligence with the ability to cope with real-life challenges.
“Crudely taking IQ as a metric to divide up individuals can be misleading, because high-functioning sounds like you are doing really well, when in fact you’re not,” says cognitive psychologist Tony Charman, [former] professor of autism education at the University of London.
A person who scores 125 on an IQ test — and thus considered high-functioning — may in fact be considerably impaired in daily activities.
and, confirming the point made earlier
A population study … looked at the association between autism traits and intelligence [which] were both stable over time, but there was only a modest association between the two, suggesting that autism traits are independent of intellectual functioning.
What does level of functioning mean in autism research?
In autism research, autistics’ level of functioning is most often judged according to scores on specific tests of IQ (e.g., Wechsler) or developmental level (Mullen, Bayley, sometimes the Vineland) at a specific time.
The reported threshold dividing “high” from “low” functioning ranges from 50 to 90–at least in papers I’ve read so far; the actual range might be even greater. Those are IQ or IQ-type scores with a mean of 100 and a standard deviation of 15. So the threshold, the line dividing “high” from “low” functioning in autism research, is almost three SDs wide. Fall into that impressive span, and you may be high or you may be low functioning, depending on who you ask.
If 90 is the threshold, then about 25% of the entire population (autistic, nonautistic, everyone) is low-functioning. If the more common threshold of 85 is chosen, then about 16% of everyone is low-functioning.
70 is the threshold often considered to be standard even if in reality, if you read the literature, the threshold varies dramatically. But there are different tests and within commonly-used tests there are different ways to set a threshold, even when the threshold is numerically set at 70.
Using the cutoff of 80 suggested in the Simons article, by the way, would mean that about 9% of autistic people are “low-functioning.”
My take on all of this is that the autism “functioning” labels so freely bandied about are misleading, inconsistent, and not really all that useful. I think we would be wise to simply drop the concept and stop using this terminology.