Comparing the Visual Analog Scale and the Numerical Rating Scale in Patient-reported Outcomes in Psoriatic Arthritis

Abstract

Objective: Patient self-report scales are invaluable in psoriatic arthritis (PsA), as they allow physicians to rapidly assess patient perspectives of disease activity. We aimed to assess the agreement of the visual analog scale (VAS), a 100-mm horizontal line, and the numerical rating scale (NRS), a 21-point scale ranging from 0 to 10 in increments of 0.5, in patients with PsA.

Methods: Data were collected prospectively across 3 UK hospital trusts from 2018 to 2019. All patients completed the VAS and NRS for pain, arthritis, skin psoriasis (PsO), and global disease activity. A subset completed an identical pack 1 week later. Demographic and clinical data were also collected. Agreement was assessed using medians and the Bland-Altman method. Intraclass correlation coefficients (ICCs) were used to assess test-retest reliability. Spearman rank correlation coefficients were used to assess dependency between scale scores and clinical variables.

Results: Two hundred ten patients completed the study; 1 withdrew consent. Thus, 209 were analyzed. For pain, arthritis, skin PsO, and global disease activity, the difference between the VAS and NRS lay mostly within 1.96 SD of the mean, suggesting reasonable agreement between the 2 scales. Among the patients, 64.1% preferred the NRS. The ICCs demonstrated excellent test-retest reliability for both VAS and NRS. Higher VAS and NRS scores were associated with increased tender/swollen joint count, poorer functional status, and greater life impact.

Conclusion: The VAS and NRS show reasonable agreement in key patient-reported outcomes in PsA. Results from both scales are correlated with disease severity and life impact.

Keywords: numerical rating scale; patient-reported outcomes; psoriatic arthritis; self-assessment; visual analog scale.