In the receiver operating characteristic paradigm the observer assigns a single rating to
each image and the location of the perceived abnormality, if any, is ignored. In the free-
response receiver operating characteristic paradigm the observer is free to mark and rate as
many suspicious regions as are considered clinically reportable. Credit for a correct
localization is given only if a mark is sufficiently close to an actual lesion; otherwise, the
observer's mark is scored as a location-level false positive. Until fairly recently there existed …