Which Score for What? Operationalizing Standardized Cognitive Test Performance for the Assessment of Change.
Use SB5 ability scores, not IQ, to see true cognitive change in clients with IDD.
01Research in Context
What this study did
Farmer et al. (2025) asked which Stanford-Binet score best shows real cognitive change in people with IDD. They compared four score types: IQ, age-equivalent, raw, and ability scores. The team used a math model to see which one tracked within-person growth most clearly.
What they found
Ability scores won. They picked up small gains or losses that other scores missed. IQ and age-equivalent scores often stayed flat even when the person had actually improved.
How this fits with other research
Cornish et al. (2012) already told us to watch growth scores, not just IQ. Cristan gives the exact tool to do it with the SB5.
M et al. (2007, 2015) built the quick RADD battery because long tests floor out in severe IDD. Cristan agrees: floor-friendly ability scores beat IQ when you track change.
Papadopoulos et al. (2013) showed that kids with ASD can get very different IQs on similar tests. Cristan says ability scores are less jumpy, so you trust the change you see.
Why it matters
If you re-test a client after an intervention, switch to SB5 ability scores. One click in the scoring software gives you a number that actually moves when learning happens. You will spot progress faster and avoid false "no change" reports to families or funders.
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02At a glance
03Original abstract
Developmental domains, such as cognitive, language, and motor, are key concepts of interest in longitudinal studies of intellectual and developmental disabilities (IDD). Normative scores (e.g., IQ) are often used to operationalize performance on standardized tests of these concepts, but it is the interval-distributed person-ability scores that are intended for the assessment of within-individual change. Here we illustrate the use and interpretation of several Stanford Binet, 5th Edition score types (IQ, extended IQ, Z-normalized raw score, developmental quotient, raw sum score, age equivalent, and ability score) using data from two longitudinal studies of rare genetic conditions associated with IDD. We found that, although normality assumptions were tenuous for all score types, floor effects led to model unsuitability for longitudinal analysis of most types of norm-referenced scores, and that the validity of interpretation with respect to individual change was best for ability scores.
American journal on intellectual and developmental disabilities, 2025 · doi:10.1007/s11136-022-03297-7