Evaluating motor function in children with Down syndrome: validity of the GMFM

The Gross Motor Function Measure (GMFM) was developed and validated originally by Russell and colleagues as an evaluative assessment of gross motor function in children with cerebral palsy (CP). The present study reports the results of reliability and validity testing of the GMFM for use with children with Down syndrome (DS). One hundred and twenty-three children with DS were assessed twice over a 6-month period, using the GMFM and the motor scale of the Bayley Scales of Infant Development - second edition (BSID-II). In addition to the usual method of scoring the GMFM using only observed motor behaviours (standard score), parent reports of children's activities not seen by the assessor on the day of testing were also obtained and a second score (reported score) was calculated for each GMFM assessment. Test-retest and interrater reliabilities were excellent (all >0.90). Observed correlations between change on GMFM and judgements of change made independently by parents, intervenors, and masked video raters were lower than hypothesized. However, the pattern of change scores in predefined age and severity subgroups supported the contention that the GMFM was able to detect differential amounts of change as predicted. The GMFM was shown to be relatively more responsive to change in gross motor function than the motor scale of the BSID-II. The 'reported' scores on the GMFM demonstrated better evidence of reliability, validity, and responsiveness than the standard scoring method and this approach is recommended for use when assessing children with DS.