a1 Harvard Institute of Psychiatric Epidemiology and Genetics, Harvard Medical School Department of Psychiatry at the Massachusetts Medical Health Center, Department of Epidemiology, Harvard School of Public Health and Pediatric Psychopharmacology Unit, Psychiatry Service, Massachusetts General Hospital, Boston, Brockton–West Roxbury Veterans Affairs Medical Center, Brockton, MA; National Institute of Mental Health Extramural Research Program, National Institute of Mental Health Intramural Research Program, Bethesda and Department of Psychiatry, Johns Hopkins University, Baltimore, MD; Department of Psychiatry, Washington University, St Louis, MO; Department of Psychiatry, Indiana University, IN; Department of Psychiatry, Columbia University, New York, NY; and Medical College of Georgia, Augusta, GA, USA
The dominant, contemporary paradigm for developing and refining diagnoses relies heavily on assessing reliability with kappa coefficients and virtually ignores a core component of psychometric practice: the theory of latent structures. This article describes a psychometric approach 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 psychiatric interview designed by the NIMH Genetics Initiative for genetic studies of schizophrenia and bipolar disorder. Our results show that sensitivity and specificity were excellent for both DSM-III-R and RDC diagnoses of major depression, bipolar disorder, and schizophrenia. In contrast, diagnostic accuracy was substantially lower for subtypes of schizoaffective disorder – especially for the DSM-III-R definitions. Both the bipolar and depressed subtypes of DSM-III-R schizoaffective disorder had excellent specificity but poor sensitivity. The RDC definitions also had excellent specificity but were more sensitive than the DSM-III-R schizoaffective diagnoses. The source of low sensitivity for schizoaffective subtypes differed for the two diagnostic systems. For RDC 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 schizophrenia, but not with each other.
c1 Address for correspondence: Dr Stephen V. Faraone, Psychiatry Service (116A), Veterans Affairs Medical Center, 940 Belmont Street, Brockton, MA 02401, USA.