The Spanish Version of the Functional Rating Index in Patients With Low Back Pain: Preliminary Results of the Validation Study

Abstract

Objective: To assess the reliability, validity, and the psychometric properties of the Spanish version of the Functional Rating Index (Sp-FRI) in a preliminary cohort of patients with low back pain (LBP). Design: Prospective observational multicenter study. Setting: Outpatient physical therapy clinics and units from public and private settings. Participants: Patients with LBP (N=22; 52.5±12.5y) entered the study. Interventions: The translation and cross-cultural adaptation were performed following international guidelines through a 5-step procedure. Main Outcome Measures: The Sp-FRI was administered along with the Spanish version of Roland-Morris Disability Questionnaire (Sp-RMDQ) and numeric pain rating scale (NPRS) index. Preliminary testing included readability, comprehensibility, ceiling and floor effects, reliability, and validity. Statistical analysis was based on the Fernandez-Huerta index, and the calculation of Cronbach alpha, intraclass correlation coefficient (ICC), and Spearmanś correlation coefficient, respectively. All patients completed the Sp-FRI again after 1-2 days to assess its test-retest reliability. Results: None of the participants requested clarification of any of the items at the time of completion. The test-retest reliability of the FRI score was substantial (ICC 0.77). Cronbach alpha was 0.859. Spearman correlation coefficient between Sp-FRI and Sp-RMDQ was 0.66; P<.0001, and between Sp-FRI and NPRS was 0.66; P<.0001. No ceiling or floor effects were detected. Conclusions: In light of these preliminary data, the Sp-FRI appears to be linguistically accurate and has been adapted to the Spanish-speaking population. It demonstrated reliability and validity and is suitable for clinical and research use among Spanish patients with LBP, with an acceptable degree of internal consistency and concurrent validity. Keywords: Cross-cultural comparison, Funtional rating index, Low back pain, Psychometrics, Rehabilitation, Translations