Measurement invariance in the assessment of people with an intellectual disability

Abstract

Intellectual assessment is central to the process of diagnosing an intellectual disability and the assessment process needs to be valid and reliable. One fundamental aspect of validity is that of measurement invariance, i.e. that the assessment measures the same thing in different populations. There are reasons to believe that measurement invariance of the Wechsler scales may not hold for people with an intellectual disability. Many of the issues which may influence factorial invariance are common to all versions of the scales. The present study, therefore, explored the factorial validity of the WAIS-III as used with people with an intellectual disability. Confirmatory factor analysis was used to assess goodness of fit of the proposed four factor model using 13 and 11 subtests. None of the indices used suggested a good fit for the model, indicating a lack of factorial validity and suggesting a lack of measurement invariance of the assessment with people with an intellectual disability. Several explanations for this and implications for other intellectual assessments were discussed.

Screening for offenders with an intellectual disability: The validity of the Learning Disability Screening Questionnaire

“…BPS, 2003).The aim of screening tools in criminal justice services is to provide an indication as to whether someone is likely to have an intellectual disability or not. As with any good assessment tool, good screening tools, need to have strong psychometric properties, including reliability, validity, standardisation with the group it is designed to be used with (Glascoe, 2005) and measurement invariance (MacLean, McKenzie, Kidd, Murray, & Schwannauer, 2011). It should also be quick and straightforward to use and have good sensitivity and specificity.…”

De IQ-score in twijfel getrokken: Evolutie naar een multidimensioneel cognitief vaardigheidsprofiel

“…Daarnaast werden de psychometrische kwaliteiten van de IQ-testen in twijfel getrokken wanneer deze gebruikt worden bij personen met een intellectuele disfunctie [44, p. 39]. De factorstructuur van de Wechsler-schalen blijkt bijvoorbeeld immers niet stand te houden binnen deze groep [45,46] en aan het lagere einde van het continuüm lijken de testen significant minder te kunnen differentiëren [45].…”

Intelligent Diagnosing of Intellectual Disabilities in Offenders: Food for Thought

“…The Wechsler Adult and Child Intelligence Scales have, for instance, evolved from assessing two cognitive abilities (i.e., verbal and performance intelligence) to assessing four cognitive abilities (i.e., verbal comprehension, perceptual organization, working memory, and processing speed). Although these aforementioned four-factor models are still far from flawless (MacLean, McKenzie, Kidd, Murray, & Schwannauer, 2011), this is an evolution that should be acclaimed given the extensive and still growing factor analytic work challenging any two-factor model of intelligence model (e.g., Carroll, 1993). Despite the promising and ever-evolving intelligence research, a possible first pitfall is worth mentioning: far too many people are tempted to equate the factor structure of such instruments with intelligence; the instrument becomes the underlying construct.…”