Measuring Change During Intervention Using Norm-Referenced, Standardized Measures: A Comparison of Raw Scores, Standard Scores, Age Equivalents, and Growth Scale Values From the Preschool Language Scales–Fifth Edition

Abstract

Purpose: Norm-referenced, standardized measures are tools designed to characterize a child's abilities relative to their same-age peers, but they also have been used to measure changes in skills during intervention. This study compared the psychometric properties of four types of available scores from one commonly used standardized measure, the Preschool Language Scales–Fifth Edition (PLS-5), to detect changes in children's language skills during and after a language intervention. Method: This study included data from 110 autistic children aged 18–48 months whose mother participated in an 8-week parent-mediated language intervention. Children's language skills were measured at 3 time points using the PLS-5. Changes in children's expressive and receptive language skills were calculated using raw scores, standard scores, age equivalents, and growth scale values (GSVs). Results: Analysis of raw scores, age equivalents, and GSVs indicated significant improvement in the scores of autistic children in both receptive and expressive language throughout the study (i.e., during the intervention period and in the 3-month period after the intervention). Standard scores suggested improvement only in the receptive language scale during the intervention period. Standard scores showed a floor effect for children who scored at −3 SD below the mean. Conclusions: Findings suggested that GSVs were not only psychometrically sound but also the most sensitive measure of direct changes in skills compared to raw, standard, and age-equivalent scores. Floor effects may limit the sensitivity of standard scores to detect changes in children's skills. Strengths, limitations, and interpretations of each of the scoring approaches in measuring changes in skills during intervention were discussed. Supplemental Material: https://doi.org/10.23641/asha.21498522