The internal structure of Brazilian versions of disability questionnaires in patients with chronic low back pain: A cross-sectional study

Background: Structural validity refers to the degree to which the scores of a questionnaire or scale are an adequate reflection of the construct to be measured. The aim of this study was to perform the analysis of the structural validity of the Roland-Morris Disability Questionnaire (RMDQ), Oswestry Disability Index (ODI), Quebec Back Pain Disability Scale (QBPDS), and Bournemouth Questionnaire (BQ) in Brazilian respondents with chronic low back pain. Methods: A cross-sectional study was conducted. The sample was composed by respondents with non-specific chronic low back pain (score >= 3 points on the 11-point Numerical Pain Rating Scale). The internal structure (number of domains and items) of the Brazilian versions of the RMDQ, the ODI, the QBPDS, and the BQ were analyzed by the confirmatory factor analysis. Results: Two hundred and twenty-two patients were included. Most of the sample consisted of women and overweight. The RMDQ and ODI have a one-dimensional structure and acceptable values for all confirmatory factor analysis fit indices. The QBPDS with 4 domains and 20 items showed the best values of the fit indices. In addition, we did not identify an internal structure for the BQ supported by the confirmatory factor analysis. Conclusion: The ODI and RMDQ present valid internal structure with 1 domain (disability). The QBPDS has a valid internal structure with 4 domains (rest, prolonged postures, ambulation/reach, and bending/carrying). The BQ does not have a well-defined internal structure.