Operating characteristics predicted by models for diagnostic tasks involving lesion localization

In 1996 Swensson published an observer model that predicted receiver operating characteristic (ROC), localization ROC (LROC), free-response ROC (FROC) and alternative FROC (AFROC) curves, thereby achieving "unification" of different observer performance paradigms. More recently a model termed initial detection and candidate analysis (IDCA) has been proposed for fitting computer aided detection (CAD) generated FROC data, and recently a search model for human observer FROC data has been proposed. The purpose of this study was to derive IDCA and the search model based expressions for operating characteristics, and to compare the predictions to the Swensson model. For three out of four mammography CAD data sets all models yielded good fits in the high-confidence region, i.e., near the lower end of the plots. The search model and IDCA tended to better fit the data in the low-confidence region, i.e., near the upper end of the plots, particularly for FROC curves for which the Swensson model predictions departed markedly from the data. For one data set none of the models yielded satisfactory fits. A unique characteristic of search model and IDCA predicted operating characteristics is that the operating point is not allowed to move continuously to the lowest confidence limit of the corresponding Swensson model curves. This prediction is actually observed in the CAD raw data and it is the primary reason for the poor FROC fits of the Swensson model in the low-confidence region.