Matching strategies in cognitive research with individuals with high-functioning autism: current practices, instrument biases, and recommendations.
Stop using PPVT, BPVS, or Raven to match IQ in autism research—Wechsler scales are the only valid choice.
01Research in Context
What this study did
Mottron (2004) looked at every autism study that matched groups by IQ. He checked which tests researchers used. He compared scores from PPVT, BPVS, Raven matrices, and Wechsler scales in high-functioning clients.
What they found
The quick vocabulary and matrix tests gave IQ scores that were too high. Only Wechsler scales gave true scores. Using the wrong test can make groups look equal when they are not.
How this fits with other research
Symons et al. (2005) built on this work. They showed you can save time by using short Wechsler forms and still keep 80-90 % accuracy with autistic clients.
Mulder et al. (2020) push the idea further. They found IQ does not predict daily living skills, so matching only by Wechsler IQ is still not enough.
Magiati et al. (2001) saw the same problem in preschoolers. Switching tests could swing scores by 20 points, foreshadowing Laurent’s larger warning.
Why it matters
If you run social-skills groups or compare interventions, recheck your matching method. Drop PPVT or Raven for IQ pairing. Use Wechsler full or short form, then add an adaptive measure. This guards against false group equality and makes your outcomes believable.
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02At a glance
03Original abstract
A meta-analysis was performed on the 133 cognitive and behavioral papers in autism using comparison groups in the 1999-2002 period. High-functioning (average IQ: 84.7), adolescents (average, 14.4 years) are largely dominant. IQ is the most frequent matching variable in use (51.2%). The instruments that are most frequently used to determine IQ or general level are Wechsler scales (46.9%), British Picture Vocabulary Scale (BPVS; 22.3%), and Raven Progressive Matrices (RPM; 16.9%). In order to determine if these instruments were equivalent when applied to individuals with pervasive developmental disorders (PDDs), Wechsler IQ, EVIP (a French Canadian translation of the BPVS), and RPM were given to a group of 14 individuals with autism and 12 with Asperger syndrome. Comparison of Wechsler and RPM IQs values, expressed as percentiles, to percentile values of EVIP score revealed that EVIP (and to a lesser extent RPM) considerably overestimates the level of all PDD participants as compared to Wechsler Verbal IQ (VIQ), Performance IQ (PIQ), or Full-Scale IQ (FSIQ), whereas these instruments are reported to be strongly correlated in typically developing individuals. This study reveals that identification of objects from a verbal label--the BPVS-PPVT-EVIP task--is a peak of ability in high functioning individuals with PDDs. This peak of ability, even superior to that of block design, has a detrimental effect on matching based on this instrument. A recommendation to replace BPVS/PPVT/EVIP or RPM by Wechsler scale as a basis of IQ/level matching is provided. Accordingly, the former instruments are a potential source of type-1 (for cognitive deficits) or type-2 (for cognitive hyperfunctioning) errors.
Journal of autism and developmental disorders, 2004 · doi:10.1023/b:jadd.0000018070.88380.83