Key outcomes in rheumatoid arthritis (RA) are evaluated with multi-item ratings scales such as the Health Assessment Questionnaire (HAQ) and visual analog scales (VAS) such as pain and patient and physician global. As VAS scales are easy to use and particularly effective in research and patient care, we studied the characteristics, association, and psychometric properties of a VAS function scale (VAS-F) to determine if it could be used in RA studies and clinical practice.
A total of 394 patients with RA completed the HAQ, the HAQ-II, and a VAS functional scale. In addition, they completed standard assessments of pain, global, fatigue, sleep problems, joint count, and the Medical Outcome Study Short-Form 36 (SF-36) physical component summary score (PCS) and vitality and total pain scores.
The HAQ-II was correlated with VAS-F at 0.76, but distributional characteristics of the HAQ and VAS-F differed, as the VAS-F scale results contained more higher scores as well as more lower scores compared with the HAQ-II and HAQ. Kendall's tau concordance analyses indicated that VAS scales were more concordant with other VAS than with non-VAS scales. Concordance of VAS-F was greatest with VAS global and was similar overall with VAS pain, sleep disturbance, fatigue, and quality of life. By contrast, the PCS, a multi-item scale, was more concordant with HAQ-II and HAQ. There was little to no difference between the VAS-F and the 2 HAQ with regard to concordance with the multi-item joint count, SF-36 vitality, and SF-36 total pain.
The distribution differences between HAQ and HAQ-II and the VAS-F suggest that patients do not see minor limitations as problematic, but rate major limitations as being particularly limiting and worthy of high ratings. A VAS functional scale represents a patient-weighted functional assessment in which additional interpretation is given to the meaning of the limitations by the patient. VAS-F scales may be suitable for use in the clinic and in research. However, studies to assess sensitivity to change are required to determine the appropriate role of this scale.