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

The Gross Motor Function Measure (GMFM) was developed and validated origina lly by Russell and colleagues as an evaluative assessment of gross motor fu nction in children with cerebral palsy (CP). The present study reports the results of reliability and validity testing of the GMFM for use with childr en with Down syndrome (DS). One hundred and twenty-three children with DS w ere assessed twice over a 6-month period, using the GMFM and the motor scal e of the Bayley Scales of Infant Development - second edition (BSID-II). In addition to the usual method of scoring the GMFM. using only observed moto r 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 correla tions between change on GMFM and judgements of change made independently by parents, interveners, and masked video raters were lower than hypothesized . However, the pattern of change scores in predefined age and severity subg roups supported the contention that the GMFM was able to detect differentia l 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 BS ID-II. The 'reported' scores on the GMFM demonstrated better evidence of re liability, validity, and responsiveness than the standard scoring method an d this approach is recommended for use when assessing children with DS.