POS1084 COMPARISON OF NUMERICAL RATING SCALE (NRS) AND VISUAL ANALOGUE SCALE (VAS) IN THE PATIENT REPORTED OUTCOME MEASURES OF 3VAS AND 4VAS IN PSORIATIC ARTHRITIS

Abstract

Background:There is a recognised need for a feasible continuous composite measure in routine clinical care for psoriatic arthritis (PsA). Two multidimensional composite Visual Analogue Scales (VAS) have been proposed; the 3 and 4VAS1, but there may be some advantages to using a numerical rating scale (NRS) over VAS in patient reported outcomes. VAS is a 100mm horizontal line, and the NRS a 21-point scale ranging from 0 to 10 in increments of 0.5. NRS are simple and faster to score, less susceptible to measurement error and may reduce the floor and ceiling effects, whereby patients avoid using the extremes of the scale. A previous study has demonstrated good agreement between VAS and NRS for the separate patient reported outcome measures in PsA, which correlate with disease severity and life impact.2Objectives:To test the performance of NRS, compared with VAS, in the composite 3 and 4VAS scores.Methods:Data were collected prospectively across three UK hospital trusts from 2018-2019, as part of a study assessing the use of NRS in patient reported outcome measures in PsA.2 Patients completed the VAS and NRS for pain, arthritis, skin psoriasis, and global disease activity. The 3 VAS comprises of a physician global VAS, patient global VAS and patient skin VAS and the 4 VAS comprises of the physician global VAS, patient pain VAS, joint VAS and skin VAS. NRS and VAS versions of the patient reported measures were tested. Physician global scores were not available from the study data, therefore only the patient reported components are included. Agreement between the scales was assessed using the intraclass correlation coefficients (ICCs), with a two-way mixed absolute agreement model, and Bland-Altman plots. Spearman’s rank correlation coefficients were used to assess dependency between scale scores and clinical parameters including tender and swollen joint count, PsAID12 and HAQDI.Results:Data from 209 patients were analysed. 60.0% were male, with mean age of 51.7 years and median PsA duration of 7.0 years. Mean 3VAS score was 3.57 and the mean NRS-3VAS was 3.79, with ICC 0.98 (95% CI 0.96-0.98). Mean 4VAS was 3.71 and NRS-4VAS was 3.90 with ICC 0.98 (95% CI 0.97-0.98). Average NRS scores were slightly higher than VAS scores. The Bland-Altman plots comparing NRS and VAS for the patient-reported components of 3VAS and 4VAS are demonstrated in Figure 1. 64.1% patients reported a preference for NRS over VAS. Correlation of the 3/4VAS with PSAID, HAQ and joints counts are reported in Table 1. Visual representation of the NRS and VAS scales for 3VAS and 4VAS as histograms demonstrated that there is marginally less floor effect using NRS compared to VAS.Conclusion:There is good agreement between VAS and NRS for the patient-reported components of 3VAS and 4VAS, supporting that VAS scores are reproducible as NRS scores. Both NRS and VAS versions of the 3 and 4VAS scales correlate with disease activity and life impact.2 There may be advantages in testing the 3/4VAS as NRS moving forward.