There is disagreement in the literature regarding which scales to use in pain measurement. The difference has usually been between nonverbal scales, such as visual analog scales and verbal ones, which usually provide only a limited number of response categories. A 12-week, randomized, double-blind naproxen sodium (500 mg bid) and placebo-controlled trial using the hip osteoarthritis (OA) flare-up pain mode, in which pain was measured on both visual analog and categorical scales simultaneously, was analyzed. The authors found a good correlation (> 0.995) between the time-series average of the unconstrained visual analog scale and a 5-point categorical scale pain measurement in the osteoarthritis pain model in both active and placebo treatment arms. However, for individuals, there is a wide range of VAS responses for each categorical score, with overlaps between categories. The visual analog and categorical scales appear as effective in determining average osteoarthritis pain. However, a combined metric scale for pain measurement that provides the subject with multiple cues may improve communication and concordance between scales for individual pain determination.

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The results demonstrated no gender difference in response to placebo. These results were obtained from the post-third molar extraction situation, in which the least possible confounding factors were present. To fully establish the generality of this phenomenon, studies should be carried out in other pain models.