Matching variables for research involving youth with Down syndrome: Leiter-R versus PPVT-4.
PPVT-4 and Leiter-R can label the same kids as ‘similar’ or ‘different’, so always report which test you used for matching.
01Research in Context
What this study did
Phillips et al. (2014) asked a simple question: if you want to match kids with Down syndrome to typically developing kids for a study, does it matter which quick IQ test you pick?
They compared two common tools: the PPVT-4, a picture-vocabulary test, and the Leiter-R, a non-verbal reasoning test. They ran both tests on the same group of youth with Down syndrome, intellectual disability, and typical development.
What they found
The two tests painted the same broad growth curves, but they gave different answers when it came time to pair kids into research groups. Swapping the test changed whether the ID and TD groups looked equal or far apart on later tasks.
How this fits with other research
Scattone et al. (2012) saw the same warning sign in autism: Leiter-R and KBIT-2 non-verbal IQ scores can differ by 10–20 points in the same child. Both papers shout the same lesson—never treat IQ tests as interchangeable.
Wuang et al. (2012) compared three motor tests for preschoolers with ID and also picked one clear winner (PDMS-2). Allyson’s cognitive-tool story mirrors that motor-tool story: head-to-head trials often reveal a ‘better’ match for group work.
Takahashi et al. (2023) meta-analysis shows large movement deficits between ID and TD kids. Their numbers rest on studies that matched groups with different tools; Allyson warns that choice of tool could shrink or inflate those very gaps.
Why it matters
Next time you read an ID-TD comparison, check which IQ test the authors used. If you run your own matching, give both PPVT-4 and Leiter-R, then pick the one that gives you the tightest, fairest pairs. Your decision can flip whether a later treatment looks like it works or not.
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02At a glance
03Original abstract
Much of what is known about the cognitive profile of Down syndrome (DS) is based on using either receptive vocabulary (e.g., PPTV-4) or nonverbal ability (e.g., Leiter-R) as a baseline to represent cognitive developmental level. In the present study, we examined the relation between these two measures in youth with DS, with non-DS intellectual disability (ID), and with typical development (TD). We also examined the degree to which these two measures produce similar results when used as a group matching variable. In a cross-sectional developmental trajectory analysis, we found that the relation between PPVT-4 and Leiter-R was largely similar across groups. However, when contrasting PPVT-4 and Leiter-R as alternate matching variables, the pattern of results was not always the same. When matched on Leiter-R or PPVT-4, the group with DS performed below that of the groups with ID and TD on receptive grammar and below the group with TD on category learning. When matched on the PPVT-4, the group with ID performed below that of the group with TD on receptive grammar and category learning, but these differences between the groups with ID and TD were not found when matched on the Leiter-R. The results of the study suggest that the PPVT-4 and Leiter-R are interchangeable at least for some outcome measures for comparing youth with DS and TD, but they may produce different results when comparing youth with ID and TD.
Research in developmental disabilities, 2014 · doi:10.1016/j.ridd.2013.11.016