The diagnostic instruments used in surveys involving interviewing of respondents fall into two categories: fully structured interviews such as the Diagnostic Interview Schedule (DIS)(!2) and the Composite International Diagnostic Interview (CIDI),(29 written to match exactly the diagnostic criteria of DSM-IIIR/IV and ICD-10, and semistructured interview schedules such as the Present State Examination (PSE)(!6) and the Schedules for Clinical Assessment in Neuropsychiatry (SCAN),(2!) which cover a broad range of psychopathology and elicit data that can be processed by alternative diagnostic algorithms. While the former can be applied by trained lay interviewers, the latter require clinical judgement and are usually administered by clinicians.
The DIS/CIDI type of instrument is reliable and capable of generating standard diagnoses in a single-phase survey design. However, the range of psychopathology covered is restricted to the diagnostic system to which it is linked, and its clinical validity is open to question because symptoms may not be reported accurately or impairment may be underestimated by the respondent. In contrast, the PSE/SCAN type of interview allows a greater amount of psychopathological data to be elicited but its use in epidemiological studies presupposes the availability of clinically skilled and trained interviewers. While SCAN and other similar interviews are suitable as second-stage diagnostic instruments, there is still a need for a relatively simple and effective screening procedure for case-finding of schizophrenia in field surveys.
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