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DEFINITION OF EFFICIENCY INDICES FOR THREE-CATEGORY DIAGNOSTIC TESTS

Vol XIV, No. 2, 2014 Comments (0)

Teresa RIVAS* & Francisco Félix CABALLERO2,3
1 Department of Psychobiology and Methodology of Behavioral Sciences, University of Málaga. 29071 Málaga (Spain) 1
2 Department of Psychiatry. Universidad Autónoma de Madrid. Arzobispo Morcillo, 4. 28029 Madrid (Spain)
3 Instituto de Salud Carlos III, Centro de Investigación Biomédica en Red de Salud Mental. CIBERSAM, Spain.

Abstract
In the context of diagnostic tests, this paper presents two indices to analyse the efficiency of a Three-Category Classification established by a diagnostic test (criterion variable) and two cut-off scores (classifier) determined on test scores (predictor variable). The Index based on the Projected Surface (IPS) is defined for any classifier. The Index based on the Tetrahedron Volume (ITV) is defined only for classifiers satisfying determined conditions. IPS and ITV assume values between 0 and 1. To define these indices, the Index based on Area Under the ROC Curve (AUC) associated with a classifier for Two-Category ROC analysis is extended for three categories. These indices are calculated and interpreted in an example proposed, from answers given by a group of females (n = 778) to a test and a diagnostic criteria. These results are compared with results obtained using other indices which evaluate efficiency of a multi-category classification established by more than one cut-off score.

Keywords: diagnostic test; efficiency indices; ROC analysis; three-category classification; cut-off scores

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