title: Criterion validity of the GMFM-66 item set and the GMFM-66 basal and ceiling approaches for estimating GMFM-66 scores.
abstract: OBJECTIVE
  The aim of this study was to compare the accuracy of two abbreviated approaches for estimating Gross Motor Function Measure 66 (GMFM-66) scores against the full GMFM-66 and to explore their strengths and limitations.
  
  
  METHODS
  An existing dataset (n=224) comprising children aged 1 to 13 years (mean age 6y 11mo, SD 4y 6mo; 132 males, 92 females) with cerebral palsy (CP) of all Gross Motor Function Classification System (GMFCS) levels was used to compare the validity of the item set version (GMFM-66-IS) and the basal and ceiling version (GMFM-66-B&C) with the full GMFM-66 scores. Follow-up assessment at 1 year (n=109) allowed evaluation of change scores and accuracy at a single point in time.
  
  
  RESULTS
  The cross-sectional agreement was excellent for both abbreviated measures (all intraclass correlation coefficients [ICCs] >0.98). When measuring change over time, both the GMFM-66-IS and the GMFM-66-B&C showed good agreement for children with bilateral CP (ICCs >0.9). However, the GMFM-66-IS assessed change over 1 year more accurately than the GMFM-66-B&C in children with unilateral CP (ICC=0.89 vs ICC=0.58; 95% confidence intervals do not overlap).
  
  
  CONCLUSIONS
  Both approaches for estimating GMFM-66 scores are accurate at a single point in time. If the primary goal of assessment is to measure change, the full GMFM-66 should still be regarded as the criterion standard. The GMFM-66-IS should be the preferred shortened measure for children with unilateral CP.
authors: CanChild Centre for Childhood Disability Research, McMaster University, Canada.
authors: Lisa M
authors: LM
authors: Avery
authors: Dianne J
authors: DJ
authors: Russell
authors: Peter L
authors: PL
authors: Rosenbaum
mesh_terms: D000293:Adolescent; D002547:Cerebral Palsy / Q000175:diagnosis* / Q000503:physiopathology*; D002648:Child; D002657:Child Development; D002675:Child, Preschool; D004185:Disability Evaluation; D005260:Female; D006801:Humans; D007223:Infant; D008297:Male; D009048:Motor Skills; D015203:Reproducibility of Results; D012720:Severity of Illness Index; D011795:Surveys and Questionnaires / Q000592:standards*