The Roland-Morris Disability Questionnaire: one or more dimensions?

Purpose: The Roland-Morris Disability Questionnaire (RMDQ) is one of the most recommended questionnaires to assess disability. Some previous studies support the assumption that the RMDQ is a unidimensional measure; however, recent studies have suggested that this measure has more than one domain and should be considered as a multidimensional scale. Therefore, the aim of this study was to analyse the structure of the RMDQ in a large sample of patients with low back pain using two different statistical approaches.
Methods: We analysed existing datasets from previous clinical studies. We assessed unidimensionality using Rasch analysis of item fit statistics and through principle component analysis of residuals. We also performed confirmatory factor analysis (CFA) to test the hypothesis of a 3-factor solution.
Results: We included data from 2826 patients with non-specific low back pain. The average age of all participants included was 46.4 years, and half of the participants were women (50.1%). The Rasch analysis model showed that the RMDQ is unidimensional, with only two items demonstrating slight excessive positive outfit. Results from the CFA suggested poor fit to the data of a 3-factor solution.
Conclusions: We recommend that the RMDQ should still be used as a unidimensional scale for measuring disability as the only construct.