Rasch analysis of the Gross Motor Function Measure: validating the assumptions of the Rasch model to create an interval-level measure.

Abstract

To describe the Rasch analysis of the Gross Motor Function Measure (GMFM-88) and to demonstrate how the assumptions of unidimensionality, sample-free measurement, and test-free measurement were validated to create an interval level measure. Cross-sectional and longitudinal (12-mo) data from a prospective study of motor development in children with cerebral palsy (CP) were used for the analysis. Motor assessments were completed at 18 children's ambulatory rehabilitation centers in Ontario, Canada, by pediatric physical therapists trained in the use of the GMFM-88. The first 537 of 682 children enrolled into a longitudinal study of motor development in children with CP. Children had a mean age of 6.43+/-2.75 years (range, 11mo-12y) with varying types and severity of CP. Not applicable. The GMFM-88. The Rasch analysis, in conjunction with clinical decisions, identified 66 items from the GMFM-88 that formed a unidimensional measure (GMFM-66). Assumptions of sample-free and test-free measurement were confirmed, and a user-friendly scoring program was developed. The GMFM-66 is an interval-level measure of gross motor function for children with CP; it should improve the scoring, interpretation, and overall clinical and research utility over the original GMFM.