Reliability of retrospective assignment of gross motor function classification system scores

Objectives: To assess alternate forms reliability and inter-rater reliability of Gross Motor Function Classification System (GMFCS) scores. Methods: Fifty randomly selected children with cerebral palsy were divided into two groups: (1) GMFCS score assigned during gait assessment (GMFCS previously assigned) and (2) no GMFCS score assigned. Using database information, two physiotherapists independently determined GMFCS scores for 25 children from the previously assigned group, and 25 from the no score assigned group. Therapists compared their recently assigned scores for the previously assigned group, discussing discrepancies until attaining agreement. This group's consensus scores were compared to GMFCS scores assigned at time of actual assessment to calculate alternate forms reliability. Results: Between-therapist agreements were kappa = 0.84 for GMFCS previously assigned group and 0.95 for no GMFCS assigned group. Kappa agreement between direct assessment and retrospectively assigned scores for the GMFCS previously assigned group was 0.79. Conclusions: Retrospective GMFCS scores can be reliably assigned.