An experimental basis for revising the graphic rating scale for pain

Seven subjects judged the differences between electrocutaneous shocks and words from two category rating lists describing those sensations in each of two difference estimation experiments. The electrocutaneous shocks used for the two experiments were 10 suprathreshold shock intensities determined separately for each subject. There were two distinct 7-word category rating lists. Both lists shared 6 common words; however, the seventh word made the rational ordering of the two lists different. Magnitude scales of meaning for the category rating words and sensory scales for the electrocutaneous shock intensities were determined for each of the two experiments for each subject using conjoint measurement analysis. Comparisons of the sensory scales for electrocutaneous shock between the two difference estimation experiments for each subject showed that they judged the electrocutaneous shocks similarly with the two word lists. This allowed for comparisons between the scales of meaning for the words from the category rating lists. The two word lists were not equivalent. There was substantial agreement among the subjects on characteristic spacings of quantitative values for the category rating items. These results suggest that clinical rating scales used for analgesimetry should not assume homogeneity of spacing of category items. A scale incorporating our subjects' common understanding is presented.