Validity and reliability of two abbreviated versions of the gross motor function measure

Abstract

Background. The "gold standard" for measuring gross motor function in children with cerebral palsy is the 66-item Gross Motor Function Measure (GMFM-66). Objective. The purpose of this study was to estimate the validity and reliability of 2 abbreviated versions of the GMFM-66; one version involves an item set approach, and the other version involves a basal and ceiling approach. Design. This was a measurement study comprising concurrent validity, comparability, and test-retest reliability components. Methods. The study participants were 26 children who were 2 to 6 years of age and had cerebral palsy across all Gross Motor Function Classification System levels. In the first session, both abbreviated versions were administered by 2 independent raters; next, the full GMFM-66 was administered. In the second session, only the abbreviated versions were administered by the same raters. Concurrent validity, comparability of versions, and test-retest reliability were determined with intraclass correlation coefficients [ICC (2,1)]. Results. Both versions demonstrated high levels of validity, with an ICC of.99 (95% confidence interval=0.972-0.997), reflecting associations with the GMFM-66. Both versions also were shown to be highly reliable, with ICCs of greater than.98 (95% confidence interval=0.965-0.994). Limitations. A smaller-than-expected sample was recruited for this study and may be a potential limitation of the study. Conclusion. Both versions of the GMFM-66 can be used in clinical practice or research. However, the GMFM-66 with the basal and ceiling approach is recommended as the preferred abbreviated version. © 2011 American Physical Therapy Association.