The DI-PAD uses questions developed for the Diagnostic Interview for Genetic Studies (DIGS) (Nurnberger et al., 1994). This optimizes comparability with the many studies, including our PIC studies that used the more extensive DIGS questionnaire. The DI-PAD then links to the Operational Criteria Checklist for Psychotic Illness (OPCRIT). The OPCRIT is a 90-item checklist and computerized diagnostic algorithm (McGuffin et al., 1991; Williams et al., 1996), and has been successfully used in the genetic analysis of phenotypic heterogeneity in both schizophrenia (Fanous et al., 2005) and bipolar disorder (Schulze et al., 2005). OPCRIT diagnoses can be based on a variety of different systems. All GPC OPCRIT diagnoses are based on DSM-IV-TR criteria (American Psychiatric Association, 2000). The DI-PAD modules provide an efficient and consistent method to collect the required data both from patient and informant interviews and through record review. In earlier studies, we found excellent agreement (kappa = 0.8) between interviewer OPCRIT diagnoses, such as those derived from the DI-PAD, and the best-estimate lifetime consensus procedure (Azevedo et al., 1999). A team of clinicians reviewed all diagnoses. In nearly one quarter of cases, our best estimate diagnosis process supplemented OPCRIT-based diagnoses.
