DIAGNOSTIC-ACCURACY AND CONFUSABILITY ANALYSES - AN APPLICATION TO THE DIAGNOSTIC INTERVIEW FOR GENETIC-STUDIES

The dominant, contemporary paradigm for developing and refining diagno ses relies heavily on assessing reliability with kappa coefficients an d virtually ignores a core component of psychometric practice: the the ory of latent structures. This article describes a psychometric approa ch to psychiatric nosology that emphasizes the diagnostic accuracy and confusability of diagnostic categories. We apply these methods to the Diagnostic Interview for Genetic Studies (DIGS), a structured psychia tric interview designed by the NIMH Genetics Initiative for genetic st udies of schizophrenia and bipolar disorder. Our results show that sen sitivity and specificity were excellent for both DSM-III-R and RDC dia gnoses of major depression, bipolar disorder, and schizophrenia. In co ntrast, diagnostic accuracy was substantially lower for subtypes of sc hizoaffective disorder - especially for the DSM-III-R definitions. Bot h the bipolar and depressed subtypes of DSM-III-R schizoaffective diso rder had excellent specificity but poor sensitivity. The RDC definitio ns also had excellent specificity but were more sensitive than the DSM -III-R schizoaffective diagnoses. The source of low sensitivity for sc hizoaffective subtypes differed for the two diagnostic systems. For RD C criteria, the schizoaffective subtypes were frequently confused with one another; they were less frequently confused with other diagnoses. In contrast, the DSM-III-R subtypes were often confused with schizoph renia, but not with each other.