Performance of the Self-administered Psoriasis Area and Severity Index in Evaluating Clinical and Sociodemographic Subgroups of Patients With Psoriasis—Editor's Comment

This article is a welcome addition to the testing of the validity, reproducibility, and responsiveness of scales and indexes for measuring the severity of cutaneous diseases (see Bigby M, Gadenne A-S [Understanding and evaluating clinical trials. J Am Acad Dermatol. 1996;34:555-590] and Allen AM [Clinical trials in dermatology, III: measuring responses to treatment. Int J Dermatol. 1980;19:1-6]). The correlation between the PASI and SAPASI was strong-moderate (the Pearson correlation coefficients range from −1 [perfect negative correlation] to +1 [perfect positive correlation], with 0 representing no correlation). It assumes a linear relationship between the 2 variables. The degree of association is generally interpreted as follows: little if any (0-0.10), weak (0.20-0.39), weak-moderate (0.40-0.59), strong-moderate (0.60-0.79) or strong (0.80-1.00) (Glantz SA. Primer of Biostatistics. New York, NY: McGraw-Hill Co; 1992). The authors' assertion that the SAPASI can be a simple and convenient way to follow patients' responses to treatment is intriguing and deserves further testing. Although the PASI is the most widely used index in dermatology, it suffers from being difficult to calculate and interpret and from confounding area of involvement and severity. Not all of these deficiencies are overcome by the SAPASI.