To the Editor:—  I read with interest the report of Woehlck et al.  1on the use of acetazolamide in the treatment of referred pain after laparoscopic surgery. To assess postoperative pain, the authors report using a visual analog scale but state that some patients were unable to respond with a number, whereas others reported a range (e.g. , 2–3). The visual analog scale is a continuous line or band along which a subject selects a point corresponding to the intensity of pain experienced. 2From the authors’ description, one may conclude that patients were verbally rating their pain on a scale from 1 to 10. This method, although acceptable, is neither a visual analog nor a continuous measurement. Instead, the scores obtained are ordinal and, as such, should not be reported as means or analyzed using an unpaired t  test, as was done in this article. How this misunderstanding may have affected the interpretation of the results and the conclusions drawn is unclear.

Woehlck HJ, Otterson M, Yun H, Connolly LA, Eastwood D, Colpaert K: Acetazolamide reduces referred postoperative pain after laparoscopic surgery with carbon dioxide insufflation. Anesthesiology 2003; 99:924–8
Ohnhaus EE, Adler R: Methodological problems in the measurement of pain: A comparison between the verbal rating scale and the visual analogue scale. Pain 1975; 1:379–84