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


METHODS
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.


METHODS
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.


METHODS
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.


METHODS
Not applicable.


METHODS
The GMFM-88.


RESULTS
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.


CONCLUSIONS
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.
CanChild Centre for Childhood Disability Research, Institute for Applied Health Sciences, McMaster University, Hamilton, ON, Canada.
Lisa M
LM
Avery
Dianne J
DJ
Russell
Parminder S
PS
Raina
Stephen D
SD
Walter
Peter L
PL
Rosenbaum
D000465:Algorithms; D000704:Analysis of Variance; D002547:Cerebral Palsy / Q000145:classification / Q000175:diagnosis* / Q000503:physiopathology*; D002648:Child; D002657:Child Development; D002675:Child, Preschool; D003430:Cross-Sectional Studies; D003627:Data Interpretation, Statistical; D003663:Decision Trees; D005260:Female; D006801:Humans; D007223:Infant; D016013:Likelihood Functions; D008137:Longitudinal Studies; D008297:Male; D009048:Motor Skills; D009864:Ontario; D011594:Psychometrics; D012720:Severity of Illness Index