A visual analogue thermometer for measuring pain intensity.

A new instrument for measuring pain intensity--the visual analogue thermometer (VAT)--was developed to overcome limitations and disadvantages of the conventional visual analogue scale (VAS). Two studies were performed to assess the validity and utility of the VAT as compared to conventional pain instruments whose psychometric qualities are scientifically recognized. The first study was carried out with a group of 65 chronic pain patients who provided pain intensity ratings using the VAT, a standard VAS, and the McGill Pain Questionnaire. A second set of measures was obtained from a group of 243 adult healthy volunteers who quantified the intensity of a set of descriptive pain terms with the VAT, a numerical scale (NUM), and a VAS. The results of both studies support the concurrent validity of the VAT as a pain measure. When assessing changes in pain levels, the VAT was able to distinguish between different pain intensities, confirming the construct validity of the instrument. No major difference emerged in the relative sensitivity of the VAT compared to the standard VAS, both scales yielding comparable pain 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 considered equidistant on an ordinal scale. No major problem was noticed in subjects' understanding or using either the VAT, VAS, or NUM scales. When questioned about pain scale preference, a substantial number of participants preferred the VAT to the standard VAS as a means of rating pain intensity. In view of the results obtained in the present studies, it is concluded that the VAT is a valid accurate, and clinically useful tool for measuring pain. Its design makes it suitable and effective for clinical use and as an outcome measure in clinical trials.