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The authors review the recently introduced method for analyzing free-response receiver operating characteristic (FROC) observer-performance experiments. These experiments allow multiple abnormalities and observer responses per image and require correct localization for true-positive events. A fundamental plot, the alternative FROC (AFROC), is emphasized, the area under which is a natural index of performance for measuring FROC observer performance. The authors show that it is possible to analyze free-response data in more general ways. The first method, AFROC analysis, involves scoring FROC images in a different way. The second method involves a new observer-performance experiment, the free-response forced error (FFE) experiment. FROC and AFROC analysis was applied to several FROC data sets, and simultaneous FROC-AFROC-FFE experiments were performed with several radiologist observers to test the three methods. The methods were found to be in good agreement with one another.
Chakraborty et al. (Thu,) studied this question.