Patients with rheumatoid arthritis (RA) consider pain to be their main problem. The goal of this study was to evaluate validity and sensitivity to change to measure pain intensity using the MOS scale in RA patients.
Three hundred sixty-three RA subjects were included. Internal consistency of the instrument was assessed with Chronbach́s alpha, construct validity was estimated with confirmatory factor analysis and hypothesis testing and sensitivity to change was evaluated with the standard response mean and hypothesis testing.
The MOS scale showed an appropriate internal consistency (α=0.89) and confirmatory factor analysis revealed it to be a unidimensional scale. In addition, the MOS scale was strongly correlated (rho=0.86) with the visual analogue scale. Convergent validity was demonstrated with the acceptance of 83% of hypotheses a priori. MOS scale standard response mean was 0.33 and 0.21 for the visual analogue scale, pain intensity changes in scales were strongly correlated, supporting its sensitivity to change.
MOS scale is a useful instrument to measure pain intensity as well as pain relief.