A COMPARISON OF PAIN MEASUREMENT CHARACTERISTICS OF MECHANICAL VISUALANALOG 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 ex perimental pain. Separate estimates of experimental pain sensation int ensity and pain unpleasantness were obtained by each method, as were e stimates of clinical pain. Orofacial pain patients made numerical scal e and VAS ratings in response to noxious thermal stimuli (45-51 degree s C) applied for 5 sec to the forearm by a contact thermode. The; deri ved stimulus-response function was well fit as a power function only i n the case of sensory M-VAS. The power function derived from sensory M -VAS ratings predicted temperatures chosen as twice as intense as stan dard temperatures of 47 degrees C and 48 degrees C, thereby providing evidence for ratio scale characteristics of M-VAS. The stimulus-respon se function derived from sensory numerical ratings differed from that obtained with M-VAS and did not provide accurate predictions of temper atures perceived as twice intense as 47 degrees C or 48 degrees C. Bot h M-VAS and numerical rating scales produced reliably different stimul us 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-p aper VAS produced very similiar stimulus-response functions. The ratio scale properties of M-VAS combined with its ease of administration an d scoring in clinical settings offer the possibility of a simple yet p owerful pain measurement technology in both research and health care s ettings.