Persian translation and validation of the Back Pain Functional Scale

Abstract

ABSTRACTBackground: Patient-reported questionnaires provide important tools that can be utilized for the assessment of treatment efficacy in clinic and research. This study aimed to translate, cross-culturally adapt, and validate the Back Pain Functional Scale into Persian (BPFSp). Methods: In this cross-sectional and prospective cohort of adult patients with low back pain (LBP), the translation and adaptation was performed according to standardized guidelines and pretested (n = 30). Psychometric testing was conducted with 100 patients with LBP and 50 healthy subjects. Fifty patients with LBP recompleted the BPFSp at least 7 days later for test–retest reliability. Results: The Persian adapted version of the BPFS was produced and validated. No floor and ceiling effects were revealed. The Cronbach’α coefficient for internal consistency was 0.895. The test–retest reliability was excellent (ICCagreement = 0.88, CI 95%: 0.80–0.93). The standard error of measurement and smallest detectable change were 9.9% and 27.5%, respectively. Construct convergent validity was demonstrated with the Persian Functional Rating Index (r = −0.77). Criterion validity was established with the Numerical Pain Rating Scale (r = −0.67). Total BPFSp scores discriminated between patients with LBP and healthy subjects. Factor structure showed two latent factors explaining a total variance of 60.1%. Conclusion: The BPFSp presented excellent reliability and validity for assessing the functional status in Persian speaking patients with LBP.