Comparison of different models with same Area

This graph shows the performance of all three observers for the same area (0.8688).

There is strong evidence here that the main relationship is between signal-to-noise ratio and the standard deviation and not distribution. It is not entirely distribution free - its just the effect of signal-to-noise ratio swamps any difference due to distribution. In the literature, it has been shown that some extreme shaped ROC curves result in slightly larger standard deviations of the area.