A VISUAL ANALOG THERMOMETER FOR MEASURING PAIN INTENSITY

A new instrument for measuring pain intensity-the visual analogue ther mometer (VAT)-was developed to overcome limitations and disadvantages of the conventional visual analogue scale (VAS). Two studies were perf ormed to assess the validity and utility of the VAT as compared to con ventional pain intruments whose psychometric qualities are scientifica lly recognized. The first study was carried out with a group of 65 chr onic pain patients who provided pain intensity ratings using the VAT, a standard VAS, and the McGill Pain Questionnaire. A second set of mea sures was obtained from a group of 243 adult healthy volunteers who qu antified the intensity of a set of descriptive pain terms with the VA? ; a numerical scale (NUM), and a VAS. The results of both studies supp ort the concurrent validity of the VAT as a pain measure. When assessi ng changes in pain levels, the VAT was able to distinguish between dif ferent pain intensities, confirming the construct validity of the inst rument. No major difference emerged in the relative sensitivity of the VAT compared to the standard VAS, both scales yielding comparable pai n estimates. In contrast, the NUM scale tended to produce higher pain ratings. Regardless of the pain scale used, the results showed unequal differences between descriptive pain terms that are commonly consider ed equidistant on an ordinal scale. No major problem was noticed in su bjects' understanding or using either the VAT VAS, or NUM scales. When questioned about pain scale preference, a substantial number of parti cipants preferred the VAT to the standard VAS as a means of rating pai n intensity. In view of the results obtained in the present studies, i t is concluded that the VAT is a valid, accurate, and clinically usefu l tool for measuring pain. Its design makes it suitable and effective for clinical use and as an outcome measure in clinical trials.