Cross-cultural adaptation, reliability and validation of the Gillette Functional Assessment Questionnaire (FAQ) into Brazilian Portuguese in patients with cerebral palsy

BACKGROUND: The purpose of this study was to translate, cross-culturally adapt and validate the Gillette Functional Assessment Questionnaire (FAQ) into Brazilian Portuguese. METHODS: The translation and cross-cultural adaptation was carried out in accordance with international recommendations. The FAQ was applied to a sample of 102 patients diagnosed with cerebral palsy (CP). Construct validity was assessed using Spearman’s correlation coefficient (rho), and the FAQ score was correlated with the Functional Mobility Scale (FMS) and Gross Motor Function Classification Scale (GMFCS). A subsample of 50 patients was used to assess reliability using intraclass correlation coefficient (ICC), standard error of measurement (SEM) and minimum detectable difference (MDD). Ceiling and floor effects were also evaluated. RESULTS: The Brazilian version of the FAQ showed excellent test-retest reliability by the assessment of the physiotherapist (ICC = 0.99) and respondent (ICC = 0.97), as well as excellent inter-examiner reliability (ICC = 0.94). The SEM was 0.23 (physiotherapist), 0.47 (respondent) and 0.64 (inter-examiner), while the MDD was 0.64 (physiotherapist), 1.29 (respondent) and 1.76 (inter-examiner). The classification of gross motor function showed a high correlation with the FAQ applied by the physiotherapist (rho = -0.89) and by the respondent (rho = -0.87). The FMS-5 m was highly correlated with the FAQ applied by the physiotherapist and the respondent (rho = 0.88 and rho = 0.87, respectively). The FMS-50 and FMS-500 presented very high correlation with the FAQ applied by the physiotherapist (rho = 0.91 for both) and high correlation with the FAQ applied by the respondent (rho = 0.89 and rho = 0.88, respectively). The Brazilian version of the FAQ did not present the ceiling and floor effects. CONCLUSION: The FAQ presented adequate psychometric properties in patients with CP, indicating that it is possible to use it as a measure of functional gait mobility in Brazil. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12887-023-03989-0.