Deviation scores: An innovative approach to interpreting cognitive test results for individuals with intellectual disabilities.

Abstract

Students with Intellectual Disability undergo frequent cognitive testing. Testing with this population is limited by insensitivity to relative strengths and weaknesses due to floor effects. The study explored the utility of deviation scores via four case studies as a supplement to educational decision-making. Four students with Intellectual Disability completed cognitive testing. Deviation scores were calculated using age dependent raw z-score transformations to determine deviation from the standardization sample norms. The application of deviation scores highlighted true relative strengths and weaknesses for students with Intellectual Disability rather than documenting previously known deficits. The four cases studies illustrated where deviation scores could, or could not, add value above and beyond traditional scoring. Deviation scores can supplement placement and service decisions for students. Practical and psychometric considerations are reviewed. The findings highlight the usefulness of deviation scores in providing meaningful information to school- and clinic-based practitioners.