Comparing quantification of pain severity by verbal rating and numeric rating scales

Background: Researchers have reported widely varying correlations among the 3 main instruments used to quantify pain severity, Visual Analog Scale (VAS), Verbal Rating Scale (VRS), and Numeric Rating Scale (NRS), both at the level of groups and at the level of individuals. Objective: To assess the comparability of reports of pain severity using a VRS and a NRS in a spinal cord injury (SCI) sample. Methods: Data were taken from a longitudinal observational study. Patients were 168 individuals with new traumatic SCI admitted for inpatient rehabilitation who completed the VRS and NRS multiple times, each time for multiple pains as appropriate. Results: For 1,114 ratings of pain, VRS and corresponding NRS ratings were correlated weakly (Spearman correlation, rho = 0.38). For 36 individuals with at least 10 completions of paired VRS and NRS, rho ranged from -0.55 to 0.76. Variation in NRS rating for each VRS adjective was reduced by about 25% when between-patient variation was eliminated. Mean NRS ratings by VRS adjective, for patients who had used each of at least 2 adjectives at least 5 times each, showed large differences in mean NRS scores between individuals using the same VRS adjective. Conclusion: There are considerable differences between individuals in how NRS and VRS are used; there also seem to be individuals whose understanding of the meaning of the VRS adjectives is completely different from what was assumed by the creators of this VRS. Both VRS and NRS data must be used with extreme caution by SCI clinicians and researchers.