Diagnostic Assessment of Cases
In order to collect a large sample, it was essential to have an efficient and cost-effective method for phenotyping. We thus employed a polydiagnostic approach involving a diagnostic interview combined with other sources of information (e.g., medical records, informant interviews) to make final symptom determinations. The diagnostic interview instrument, the Diagnostic Interview for Psychosis and Depression (DI-PAD), was developed as an efficient and comprehensive tool for use in large-scale studies such as the GPC.19 The DI-PAD focuses on the criteria for schizophrenia, schizoaffective disorder, and bipolar disorder and is an adaptation of the psychosis, mania, depression, and other sections of the DIGS.10
DI-PAD responses are integrated with information from medical records and/or from informant interviews, and diagnoses are then formulated by the algorithms contained in the Operational Criteria Checklist for Psychotic and Affective Illness (OPCRIT) computer program.20 The OPCRIT scores 90 symptoms using diagnostic algorithms consistent with a variety of classification systems, including DSM-IV. Of note, OPCRIT algorithms incorporate items that may indicate potentially confounding factors (i.e., alcohol and substance abuse, coarse brain disease, and psychosocial stressors).