Correspondence of classifications between parents of children with cerebral palsy aged 2 to 6 years and therapists using the Gross Motor Function Classification System

AIM The aim of this study was to determine the agreement and reliability of parent report using a lay version of the Gross Motor Function Classification System (GMFCS) among children with cerebral palsy in the two youngest age bands. METHOD Data were obtained from the Canadian section of the Movement and Participation in Life Activities of Young Children study database. One hundred and thirty-two parents of two groups of children participated: children aged 2 to 4 years (35 males, 26 females; mean age 3y 2mo; SD 5mo) and children aged 4 to 6 years (39 males, 32 females; mean age 4y 11mo; SD 6mo) at the final data collection point. Therapists classified motor function using the GMFCS and parents used the GMFCS Family Report Questionnaire, with parents and therapists being masked to the others' responses. Agreement between respondents was determined using precise agreement and Cohen's unweighted kappa statistic. Reliability between respondents was determined using the intraclass correlation coefficient (ICC). RESULTS Overall, precise agreement was 77%, chance-corrected agreement was kappa = 0.70 (95% confidence interval [CI] 0.61-0.79), and reliability was ICC = 0.95 (95% CI 0.93-0.96). INTERPRETATION These values indicate substantial agreement and reliability between parents of children aged 2 to 6 years and therapists. Some parents had a tendency to rate their children as more functionally limited than did therapists, leading us to question whose the true criterion standard' rating should be.