SPURIOUS PRECISION - PROCEDURAL VALIDITY OF DIAGNOSTIC-ASSESSMENT IN PSYCHOTIC DISORDERS

Objective: Very few studies have quantified the level of agreement amo ng alternative diagnostic procedures that use a common set of fixed op erational criteria. The authors examined the procedural validity of fo ur independent methods of assigning DSM-III-R diagnoses of psychotic d isorders. Method: The research was conducted as a satellite study to t he DSM-IV Field Trial for Schizophrenia and Related Psychotic Disorder s. The setting was the National Health and Medical Research Council Sc hizophrenia Research Unit's Early Psychosis Prevention and Interventio n Centre, which focuses on first-episode psychosis. Consecutively admi tted patients (N=50) were assessed by independent raters who used four different procedures to determine a DSM-III-R diagnosis. These proced ures were 1) the diagnostic instrument developed for the DSM-IV field trial, 2) the Royal Park Multidiagnostic Instrument for Psychosis, 3) the Munich Diagnostic Checklists, and 4) a consensus DSM-III-R diagnos is assigned by a team of clinician researchers who were expert in the use of diagnostic criteria. Results: Concordance between pairs of diag nostic procedures was only moderate. Corresponding levels of percent a greement, however, ranged from 66% to 76%, with converse misclassifica tion rates of 24%-34% (assuming one procedure to be ''correct''). Conc lusions: These findings have significant research and clinical implica tions. Despite the introduction of operationally defined diagnoses, th ere remained an appreciable level of differential classification or mi sclassification arising from variability in the method of assigning th e diagnostic criteria rather than the criteria themselves. Such miscla ssification may impede neurobiological research and have harmful clini cal effects on patients with first-episode psychosis.