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Aim: The “gold standard” to measure gross motor functioning for children with cerebral palsy (CP) is the Gross Motor Function Measure (GMFM-66). The purpose of this study was to estimate the validity and reliability of two abbreviated versions (item set (GMFM-66 IS) and basal and ceiling (GMFM-66 B&C) approaches) of the GMFM-66.
Methods: Twenty-six children with CP aged 2 to 6 years across all GMFCS levels participated. At session one, both abbreviated versions were administered by two independent raters, followed by the full GMFM-66. In the subsequent session, only the abbreviated versions were administered, by the same raters. Concurrent validity, comparability between versions and test-retest reliability were determined using intraclass correlation coefficients (ICC 2,1).
Results: Both versions demonstrated high levels of validity with ICCs reflecting associations with the GMFM-66 of 0.99 (95% CIs ranging from 0.972-0.997). Both versions were also shown to be highly reliable with ICCs greater than 0.98 (95% CIs ranging from 0.965-0.994).
Interpretation: Both versions can be used in clinical practice or research. However, the GMFM-66-B&C is recommended as the preferred abbreviated version.