Comparison of the construct validity and sensitivity to change of the visual analog scale and a modified rating scale as measures of patient global assessment in rheumatoid arthritis.
OBJECTIVE
Patient global assessment (PGA) is commonly measured using a visual analog scale (VAS). The VAS asks patients to integrate many dimensions of rheumatoid arthritis (RA) activity, yet its scope is poorly defined and its endpoints are vague. We investigated whether a modified Rating Scale that used marker states and more defined endpoints would provide a more valid measure of PGA.


METHODS
In our prospective longitudinal study, 164 patients with active RA rated their global arthritis activity using the VAS and Rating Scale before and after treatment. To compare construct validity, we correlated each score with 2 reference measures of RA activity, the 28-joint count Disease Activity Score (DAS28) and the physician global assessment, and examined how each measure was associated with different aspects of RA activity, including pain, functioning, and depressive symptoms, in multivariate regression analyses. We also examined sensitivity to change.


RESULTS
Both measures were correlated with the DAS28 (r = 0.39 for VAS; r = 0.35 for Rating Scale) and physician global assessment (r = 0.41 for VAS; r = 0.26 for Rating Scale) at the baseline visit. Pain and depressive symptoms had the strongest association with the VAS, while functional limitations and depressive symptoms had the strongest association with the Rating Scale. Residual analysis showed no differences in heterogeneity of patients' ratings. VAS was more sensitive to change than the Rating Scale (standardized response means of 0.55 and 0.45).


CONCLUSIONS
As measures of PGA, the VAS and Rating Scale had comparable construct validity, but differed in which aspects of arthritis activity influenced scores. VAS was more sensitive to change.
Lati
Chili
C
Intramural Research Program, National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS), National Institutes of Health (NIH), Bethesda, Maryland 20892-1468, USA.
Guthrie
Lori C
LC
Ward
Michael M
MM
D000328:Adult; D000368:Aged; D001172:Arthritis, Rheumatoid / Q000175:diagnosis* / Q000503:physiopathology; D005260:Female; D006304:Health Status; D006801:Humans; D008297:Male; D008875:Middle Aged; D010146:Pain / Q000175:diagnosis* / Q000503:physiopathology; D010147:Pain Measurement; D011446:Prospective Studies; D011788:Quality of Life; D012044:Regression Analysis; D012680:Sensitivity and Specificity; D012720:Severity of Illness Index; D011795:Surveys and Questionnaires