Fig. 1.

Within-subject and between-subject variability of pain ratings. (A) Exemplificative data from 5 out of the 96 participants of experiment 1. Single-trial pain intensity ratings (dots) are color-coded according to stimulus energy (E1 to E4), together with the density distribution plot of each energy. (B) Receiver operating characteristic (ROC) curves show the ability of subjective ratings to discriminate stimulus energy. Area-under-the-curve (AUC) values, representing the discrimination performance, are all greater than 0.5 (P < 0.001), indicating that individual subjects were able to discriminate each pair of the four stimulus energies, even if they used different parts of the rating scale.