Back pain Knowledge and beliefs Survey (BacKS): development and assessment of measurement properties.

Objective: To develop and evaluate a new patient-reported outcome measure (PROM) to assess people's knowledge and beliefs about low back pain.

Methods: This study followed the COnsensus-based Standards for the selection of health Measurement INstruments guidelines. An 18-item preliminary version of the Back pain Knowledge and beliefs Survey (BacKS) was generated based on evidence-based key messages and current clinical guidelines for low back pain. Four items were added following input from three consumers and seven experts. Focus groups (n=9) confirmed content validity. The 22-item version was completed by 258 Australian-based adults (>18 years) with self-reported low back pain. A follow-up survey was sent 1 week later. The following measurement properties were evaluated to produce, and then assess the final version of BacKS: structural validity (exploratory factor analysis); internal consistency (Cronbach's alpha); test-retest reliability (intraclass correlation coefficient); measurement error (Smallest Detectable Change); construct validity (hypothesis tested: moderate positive Pearson correlation between BacKS and Back Beliefs Questionnaire); plus, interpretability and feasibility.

Results: The final BacKS comprised 20 items with a 2-factor structure (biomedical factor: 9 items, score ranging from 9 to 45, and self-care factor: 11 items, score ranging from 11 to 55). Internal consistency and reliability were adequate (>0.70) for each factor. Smallest detectable change was 4.4 (biomedical factor) and 7.0 (self-care factor). Our construct validity hypothesis was confirmed (Pearson correlation=0.53). No floor or ceiling effects were detected.

Conclusion: The BacKS is a valid, reliable and feasible PROM to measure knowledge and beliefs about low back pain in clinical practice and research settings.