We have to wait, patiently, for the DSM-V people to cough up their system for ranking and classifying all autistics according autism "severity." In the meantime, some recently reported data are worth mulling over.
First, here is the most recent unofficial DSM-V autism "severity" ranking-system proposal, and here is my response, including information about instruments commonly claimed to measure autism "severity." The current official DSM-V void in this area can be located here.
An increasingly prominent measure of autism "severity" is the Social Responsiveness Scale. Developed by John Constantino, it now exists in different age-range versions. Its purpose encompasses quantifying what are presumed to be autistic traits, from none on up, across the full range of humanity.
The SRS is a 65-item questionaire most often filled out by parents or teachers, whose ratings classify children according to "severity of autistic symptomology." Higher scores, above an established threshold, indicate greater autism "severity," and are therefore considered worse.
In a recently epublished high-profile paper (Roberts et al., in press), SRS scores were reported for 25 autistic children who were recruited then divided into two groups according to performance on a popular test of language abilities.
The children were about 10 years old. Sixteen autistic children classified as non-language-impaired achieved an average language ability score of ~100, right at the mean for the administered test. In contrast, nine autistic children classified as language-impaired scored ~65, more than two standard deviations lower.
I'm going to ignore the main purpose of this interesting study, which used magnetoencephalography to compare auditory evoked responses in autistics and nonautistics. Instead I'll concentrate on how this divided sample of autistic children was characterized.
Apart from language scores, the authors reported what could be considered verbal and performance intelligence, as per indexes from the latest child version of the Wechsler scales. Here the non-language-impaired autistic children scored significantly higher, with ~20-point and ~16-point advantages, respectively, over the language-impaired autistic group.
As I wrote above, Roberts et al. (in press) also reported SRS scores, described here as "dimensional symptom severity ratings."
SRS raw scores are commonly used in research, but the SRS has also been standardized, providing T-scores which account for variables such as gender and differences between raters (e.g. parents vs teachers). T-scores are standard scores with a mean of 50 and a standard deviation of 10.
While the SRS is not yet considered a diagnostic instrument, a T-score of 60, one SD above the mean, is currently the SRS-based cut-off for an autistic spectrum diagnosis. Standard scores from 60 to 75 currently indicate SRS-based "mild to moderate" autism; 76 or higher is the SRS-based "severe" autism range.
As might be predicted, the two autistic groups in Roberts et al. (in press) differed significantly on SRS T-scores; that is, they differed on autism "severity." One group scored on average 70.89, falling into the "mild to moderate" range. The other scored 81.44, a full standard deviation higher, and crossed the threshold into "severe" autism.
As wouldn't be predicted at all, the non-language-impaired autistics, who had advantages not only in language but on measures of intelligence, were the "severe" autistics, while the language-impaired children were the "mild to moderate" ones.
My wild guess is that if an autism intervention was shown in fair tests to consistently produce a reduction in SRS scores of a full standard deviation, and what's more, transported groups--however small--of autistic children from the "severe" to the "mild to moderate" SRS range, this would be considered tremendous progress.
The sample of autistic children in Roberts et al. (in press) is of course very small, as is charateristic of the bulk of the autism literature, and much can happen within such small sample. But these data aren't inconsistent with numerous other existing reports, and deserve at least a look while we wait, patiently, for the DSM-V people to proclaim on autism "severity."
You can find an uncritical short blurb about the SRS, which used to be called the "Social Reciprocity Scale," here, and a more extensive, critical description here.
Many thanks to Jennifer Stevenson for (patiently) answering my questions about the SRS. Any factual errors are entirely mine and should you find any, you should alert me immediately.
Reference:
Roberts TP, Khan SY, Rey M, Monroe JF, Cannon K, Blaskey L, Woldoff S, Qasmieh S, Gandal M, Schmidt GL, Zarnow DM, Levy SE, & Edgar JC (2010). MEG detection of delayed auditory evoked responses in autism spectrum disorders: towards an imaging biomarker for autism. Autism research : official journal of the International Society for Autism Research PMID: 20063319
Postscript: This post has been included in the 21st edition of Scientia Pro Publica.