Subject-centered free-response ROC (FROC) analysis.

PURPOSE: To develop an approach of estimating subject-centered free-response receiver operating characteristic (FROC) curve for providing patient-centered inferences regarding detection-localization characteristics of a diagnostic system.
METHODS: The authors examine properties of the conventional, target-centered, FROC curve and demonstrate that in scenarios where the diagnostic performance correlates with the total number of targets on a subject, it may lead to inadequate inferences from the perspective of possible benefits to a patient. Following solutions to patient-centered approaches in other applications, the authors define a subject-centered FROC curve and develop its formulation as a covariate-adjusted FROC curve. The authors also conduct a numerical study illustrating the relative properties of the conventional and subject-centered approach and provide an example.
RESULTS: A simple-to-implement approach for estimating the subject-centered FROC curve and its overall index can be formulated as a type of stratified FROC analysis. The authors demonstrate that when diagnostic performance is associated with the number of targets, the diagnostic system with apparently superior target-centered characteristics (conventional approach) can be actually inferior from the subject-centered perspective. The authors show that under some clinically reasonable conditions the magnitude of disagreement in results could be substantial. An example from an actual observer performance study illustrates the natural setting where the developed approach would be relevant and lead to conclusions that are contradictory to those obtained from conventional analysis.
CONCLUSIONS: The authors developed a subject-centered FROC curve and its overall index provides tools for inferences that may be relevant from a perspective of potential benefits to a patient.