A comparison of pain measurement characteristics of mechanical visual analogue and simple numerical rating scales

Numerical rating scales and mechanical visual analogue scales (M-VAS) were compared for their capacity to provide ratio scale measures of experimental pain. Separate estimates of experimental pain sensation intensity and pain unpleasantness were obtained by each method, as were estimates of clinical pain. Orofacial pain patients made numerical scale and VAS ratings in response to noxious thermal stimuli (45-51 degrees C) applied for 5 sec to the forearm by a contact thermode. The derived stimulus-response function was well fit as a power function only in the case of sensory M-VAS. The power function derived from sensory M-VAS ratings predicted temperatures chosen as twice as intense as standard temperatures of 47 degrees C and 48 degrees C, thereby providing evidence for ratio scale characteristics of M-VAS. The stimulus-response function derived from sensory numerical ratings differed from that obtained with M-VAS and did not provide accurate predictions of temperatures perceived as twice intense at 47 degrees C or 48 degrees C. Both M-VAS and numerical rating scales produced reliably different stimulus response functions for pain sensation intensity as compared to pain unpleasantness and both provided consistent measures of experimental and clinical pain intensity. Finally, both mechanical and pencil-and-paper VAS produced very similar stimulus-response functions. The ratio scale properties of M-VAS combined with its ease of administration and scoring in clinical settings offer the possibility of a simple yet powerful pain measurement technology in both research and health care settings.