15-item Roland-Morris Disability Questionnaire (RMDQ-15): structural and criterion validity on patients with chronic low back pain

BACKGROUND: The Roland-Morris Disability Questionnaire (RMDQ) is one of the most used instruments to measure self-reported disability in patients with low back pain, however, the uncertainty on which version to use may lead to inadequate disability measurement and consequently, improper management of patients with chronic low back pain. OBJECTIVE: To propose a short version of the RMDQ, compare it with the other short versions presented by the specialized literature, and identify the best internal structure of the RMDQ for the Brazilian population. METHODS: This is a cross-sectional study in which we used confirmatory factor analysis to identify the best structure of the RMDQ. We assessed 545 participants, most of which were women, aged ≥ 30 years old, single, with mean low back pain intensity ~ 5 points, and mean pain chronicity ~ 72 months. We used lavaan and semPlot packages, with implementation of a tetrachoric matrix and the robust diagonally weighted least squares extraction method. We also used fit indices chi-square/degree of freedom, comparative fit index, Tucker-Lewis index, root mean square error of approximation, and standardized root mean squared residual. For the comparison between models, we considered the structure with the lowest values of the Akaike information criterion and Bayesian information criterion. In addition, we assessed criterion validity via Spearman’s correlation coefficient to correlate the long and short versions. In this study, the 15-item structure was created through the use of modification indices to identify redundant items (9 items were excluded). RESULTS: RMDQ structure with one domain and 15 items and the structure with two domains and 16 items showed all fit indices with adequate values, but the one-dimensional version showed the lowest Akaike information criterion and Bayesian information criterion values. Regarding criterion validity, correlation between the RMDQ with 24 items and 15 items is adequate (rho = 0.954, p < 0.001). CONCLUSION: The RMDQ-15 is a short version of the RMDQ instrument with the most adequate internal structure and satisfactorily correlated with the long version of the instrument. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12891-022-05953-y.