Signal Detection Theory and Psychophysics - Andrei Gorea

d’ with unequal variancespHAreaunder ROC,Az dD a YN210.80.6d’0.40.200 0.2 0.4 0.6 0.8 1pFASometimes a measure of performance expressed as a proportion is preferred to oneexpressed as a distance. The index Az, is such a proportion and is simply D YNtransformed by the cumulative normal distribution function , i.e. (D YN ):Az is the area under the normal-model ROC curve, which increases from .5 at zerosensitivity to 1.0 for perfect performance. It is basically equal to %Correct in a 2AFCexperiment. It is a truly nonparametric index of sensitivity.