Empirical determination of thresholds for case identification: validation of the Personality Diagnostic Questionnaire-Revised.

The Personality Diagnostic Questionnaire-Revised (PDQ-R) was sent to first-degree relatives of major psychotic patients for identification of DSM-III-R personality disorders (PDs). Responses to the PDQ-R were interpreted both literally and empirically, and compared with the Structured Interview for DSM-III PDs (SIDP) as the standard. For literal interpretation, symptoms reported were counted directly for case identification using fixed DSM-III-R thresholds. The empirical approach adjusted the threshold for case identification to maximize concordance with the SIDP. Comparison of the two methods showed that using empirically determined thresholds in some scales gives better concordance with the SIDP. For the dependent and histrionic PD scales, the improvements were statistically significant. The area under the receiver operating characteristic (ROC) curve was computed for each PDQ-R scale to summarize its discriminatory capability across all thresholds. Areas under the ROC curve indicated that the schizoid, schizotypal, borderline, dependent, passive-aggressive, and histrionic PD scales in the PDQ-R have better discriminatory qualities than other PDQ-R scales.