Reliability and Validity of the Turkish Version of the Gross Motor Function Measurement (GMFM-88&66) in Children with Cerebral Palsy

Background: The gross motor function measurement is considered as the gold standard for the motor assessment of children with cerebral palsy. The aim was to carry out the cross-cultural adaptation and investigate psychometric properties. Methods: A total of 150 children with cerebral palsy aged 2-16 (mean 8.82 +/- 3.78 years; 54.7% male) included. The Gross Motor Function Measurement was adapted into Turkish. Two physiotherapies independently administered the gross motor function measurement. Internal consistency and intra/inter-rater reliability were assessed using Cronbach's alpha, intraclass-correlation-coefficient. Standard-error-of-measurement, minimal-detectible-change calculated. The Bland-Altman method was applied to estimate the measurement bias in reliability analysis. Construct validity assessed with Spearman's correlation coefficient between the gross motor function measurement and the gross motor function classification system, pediatric-evaluation-of-disability-inventory-mobility; confirmatory-factor-analysis was carried. Results: Internal-consistency (alpha: 0.997-1.00); reliability indices were excellent for total scale (intraclass-correlation-coefficient for intra-rater reliability 0.994-0.999, inter-rater reliability 0.997-0.999) and for each sub-dimension and total score. Standard-error-of-measurement was ranging 1.044-1.677, minimal-detectible-change was 2.435-5.520. Construct validity was supported by strong to excellent negative significant correlations (p < 0.05).