BACKGROUND AND AIM: Growing attention is being given to physical functioning measures to assess interventions for low back pain (LBP). The Quebec Back Pain Disability Questionnaire (QBPDS) has never been validated in Italian patients, and the aim of the study was culturally adapting and validating the Italian version of the QBPDS (QBPDS-I), to allow its use with Italian-speaking patients with chronic LBP.
METHODS: The QBPDS-I was developed by means of forward-backward translation, a final review by an expert committee and a test of the prefinal version to evaluate its comprehensibility. The psychometric testing included structural validity by exploratory factor analysis (EFA), reliability by internal consistency (Cronbach's alpha) and test-retest reliability (intraclass correlation coefficient, ICC 2.1), measurement error by calculating the minimum detectable change (MDC), construct validity by assessing hypotheses of QBPDS correlations with the Roland Morris Disability Scale (RMDQ), the Oswestry Disability Questionnaire (ODI) and a pain numerical rating scale (NRS) (Spearman's correlations).
RESULTS: It took one month to develop a consensus-based version of the QBPDS-I. The questionnaire was administered to 201 subjects with chronic LBP and was well accepted. EFA suggested a one-factor 20-item solution (first factor variance explained = 54.7%). Internal consistency (α = 0.95) and test-retest reliability (ICC = 0.90) were excellent. The MDC was 12 scale points. Construct validity was good as all of the hypotheses were met; correlations: RMDQ (r = 0.40), ODI (r = 0.48) and NRS (r = 0.44).
CONCLUSIONS: The QBPDS-I is unidimensional, reliable and valid in patients with chronic LBP. Its use is recommended for clinical and research purposes.