The validity of pain intensity measures: what do the NRS, VAS, VRS, and FPS-R measure?

Background and aims: The Numerical Rating Scale (NRS), Visual Analogue Scale (VAS), Verbal Rating Scale (VRS), and Faces Pain Scale-Revised (FPS-R) are valid measures of pain intensity. However, ratings on these measures may be influenced by factors other than pain intensity. The purpose of this study was to evaluate the influence of non-pain intensity factors on the pain intensity scales. Methods: We administered measures of pain intensity (NRS, VAS, VRS, FPS-R), pain unpleasantness, catastrophizing, depressive symptoms, and pain interference to 101 individuals with chronic lower back or knee pain. Correlation analyses examined the associations among the pain intensity scales, and regression analyses evaluated the contributions of the non-pain intensity factors (depressive symptoms, and pain unpleasantness, catastrophizing, and interference) to the VAS, VRS, and FPS-R ratings, while controlling for NRS, age, and gender. Results: Although the NRS, VAS, VRS, FPR-S, scales were strongly associated with one another, supporting their validity as measures of pain intensity, regression analyses showed that the VRS also reflected pain interference, the FPS-R also reflected pain unpleasantness, and the VAS was not associated with any of the additional non-pain intensity factors when controlling for NRS, age, and gender. Conclusions: The VAS appears to be most similar to the NRS and less influenced by non-pain intensity factors than the VRS or FPS-R. Although the VRS and FPS-R ratings both reflect pain intensity, they also contain additional information about pain interference and pain unpleasantness, respectively. These findings should be kept in mind when selecting pain measures and interpreting the results of research studies using these scales.