Using Z and age-equivalent scores to address WISC-IV floor effects for children with intellectual disability

Area of Science:

• Psychometrics
• Neurodevelopmental Disorders
• Intellectual Disability

Background:

• The Wechsler Intelligence Scale for Children - Fourth Edition (WISC-IV) often exhibits floor effects in individuals with intellectual disability.
• Z-scores and age-equivalent scores are proposed as potential solutions to mitigate these floor effects.

Purpose of the Study:

• To evaluate the efficacy of Z-scores and age-equivalent scores in addressing WISC-IV floor effects for individuals with intellectual disability.
• To compare the resulting cognitive profiles derived from these scoring methods.

Main Methods:

• Applied Z-score and age-equivalent score calculations to WISC-IV data from 198 individuals with intellectual disability.
• Utilized Bayesian confirmatory factor analysis and profile analysis.

Main Results:

• The intelligence structure in intellectual disability showed configural but not metric invariance compared to typical development.
• Z-scores and age-equivalent scores, unlike traditional scaled scores, produced average profiles similar to those seen in other neurodevelopmental disorders.
• Both alternative scoring methods successfully avoided floor effects.

Conclusions:

• Z-scores and age-equivalent scores effectively eliminate floor effects in WISC-IV assessments for individuals with intellectual disability.
• While yielding similar, not identical, profiles, age-equivalent scores may offer greater interpretability, even for those with severe intellectual disability (mean IQ < 43).