The Size of Lesions, or Point Counting as a Step Toward the Solution of the PASI Problem

Abstract

To the Editor.— In their article on disease progress in psoriasis, Marks et al¹ have stated that "there is clearly a need for better objective measures of psoriasis severity." The authors have convincingly demonstrated the problems with the assessment of the extent and severity of psoriasis, as well as the high interobserver variability. It is well known that "the human eye is notoriously poor as an estimator of area fraction."² However, this deficit can easily be overcome by the application of the long-known and remarkably simple principle of point counting, allowing area determination with astonishing accuracy. In this field of application, ie, area determination, point-counting methods with appropriately spaced grids are clearly superior to automatic and semiautomatic methods.³ As indicated earlier concerning the determination of nevus size,⁴ points, such as those represented by the crossover points of a lattice grid, allow rapid area determination. Besides the