Comparison of a verbal numeric rating scale with the visual analogue scale for the measurement of acute pain.

Abstract

To test the agreement between the visual analogue scale (VAS) and a verbal numeric rating scale (VNRS) in measuring acute pain, and measure the minimum clinically significant change in VNRS. Patients scored their pain by the VAS and the VNRS, then re-scored their pain every 30 min for up to 2 h. Patients also recorded whether their pain had improved or worsened. Agreement between scores was evaluated, and where patients scored their pain as 'a bit worse' or 'a bit better' the mean change in VNRS was calculated. A total of 309 paired observations were obtained from 79 patients. The VAS and VNRS were highly correlated (r = 0.95, 95% CI 0.94-0.96). The VNRS was significantly higher than the VAS for the paired observations, with 95% of the differences between VAS and VNRS lying between -2.3 and 1.3 cm. The minimum clinically significant difference in VNRS was 1.4 cm (95% CI 1.2-1.6). The VNRS performs as well as the VAS in assessing changes in pain. However, although the VAS and VNRS are well correlated, patients systematically score their pain higher on the VNRS, with an unacceptably wide distribution of the differences.