Factorial validity of the Supports Intensity Scale (SIS).
The SIS six-factor structure is rock-solid across gender and age, so use it freely, but watch for score dips when the adult with ID joins as a rater.
01Research in Context
What this study did
The team ran a confirmatory factor analysis on the Supports Intensity Scale.
They used data from the adults with intellectual disability across 25 states.
The goal was to see if the six-factor structure stayed solid across gender, age, and severity groups.
What they found
The six-factor model fit the data well.
It held perfectly across gender, age, and complexity of disability.
It only held loosely across severity groups, so use caution when comparing mild vs. profound scores.
How this fits with other research
Hagiwara et al. (2021) extends this work. They kept the same six-factor model but showed that adding more raters raises the score, while adding the adult with ID lowers it.
Maïano et al. (2011) used the same CFA method on a depression scale for teens with ID and also found good fit, proving the method works for different constructs.
Wilson et al. (2023) repeated the CFA story with two new wellbeing scales for adolescents, giving you more tools that passed the same psychometric test.
Why it matters
You can trust the SIS six-factor scores for planning supports, no matter the client’s gender or age.
When you compare mild vs. profound groups, remember the model is shakier—look at raw profiles, not just standard scores.
If you add the adult as a rater, expect lower numbers; balance that view with family or staff reports before you write goals.
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02At a glance
03Original abstract
The Supports Intensity Scale (SIS) was developed to provide information on the support needs of persons with intellectual disability. Our aim here was to evaluate the factorial validity of the SIS in a sample of 14,862 persons with intellectual disability. The structure of the instrument as promulgated by the developers was tested and its stability evaluated across gender, age, disability complexity, and disability severity groups. Confirmatory factor analysis supported the originally proposed subscale structure. The six-factor structure yielded strict factorial invariance across gender, age, and disability complexity, whereas invariance of factor configuration was merely established across disability severity groups. Possible explanations and implications of these findings are discussed.
American journal on intellectual and developmental disabilities, 2010 · doi:10.1352/1944-7558-115.4.327