Factorial validity of the Supports Intensity Scale (SIS)

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.