Measuring clinical pain

There are two goals in attempts to measure, the intention to describe and the intention to compare. These two functions work hand in hand and are brought to fruition in psychological and educational testing only by psychometrics that can produce person-free item calibrations and item-free person measures. The only such psychometrics that currently exist is that based on George Rasch's work. One of the consequences of using the tools Rasch left us is the Pain Scale, a rating scale that asks the person in pain to compare the intensityof his/her own pain with that he/she imagines is described by some 25 adjectives. Analyses of the responses of 53 people with chronic lower back pain to the Pain Scale using the Rasch partial-credit latent-trait model show that they were very much in agreement about the amount of hurt implied by each of the adjectives. An examination of person fit to the partial-credit model gave no hint of a response set in the data but two people did differ very much from their peers in their operational definitions of back pain and were studied separately. The evidence from these two people suggested that they either could not understand the task before them or could not get enough perspective on their pain to describe its intensity.I would like to thank Benjamin Wright and Geoff Masters for their help with this research. Drs. David J. Smith and James B. Boscardin were the first to bring my attention to the problem of measuring pain and were generous in their financial support of this work.