Case Identification In Research

example, the treating physician) are used, as with the diagnostic information recorded in case registers or in national statistics.

In order to be practicable, questionnaires should seek simple responses to unelaborated questions. However, symptoms are traditionally recognized through an assessment of mental experiences that demand quite elaborate enquiry (Brugha et al., 1999). They are usually established by a process of clinical cross-examination. This process is rather complicated since it requires the questioner to frame further questions in a flexible way in the light of the answers given by the subject. While it might be possible to encapsulate this procedure in a standard questionnaire by using a branching algorithm, it would be exhaustive and exhausting—it might require paths comprising over a dozen questions just to establish the presence of pathologically depressed mood. In these circumstances, there are clearly practical limits to the process of standardization, and it is probably better to rely on the short cuts available from using the skills of trained clinicians. Since diagnosis is built around symptoms defined and elicited in this manner, redefinition in terms of answers to much more limited questions would involve changing the concept of diagnosis itself. No one has seriously suggested that the way psychiatric symptoms are conceptualized should be changed; therefore, if a questionnaire is used, phenomena may be recorded as present when subsequent clinical enquiry might reveal otherwise, and vice versa. Nevertheless, structured questionnaires do allow lay interviewers to be used, with considerable cost savings. The Diagnostic Interview Schedule (DIS) (Robins et al., 1981) and the Composite International Diagnostic Interview (CIDI) (Robins et al., 1988) are fully structured questionnaires that have been widely used, and have good reliability.

Semi-structured research interviews are costly in clinical time, and the way in which symptoms are established makes it impossible to standardize the procedure entirely (Robins, 1995). Because of the reliance on clinical judgement and the effect this has on the choice of follow-up questions, some variability will remain. This is the price paid for greater validity, that is, the closer approximation to the clinical consensus about the nature of given symptoms. The Schedules for Clinical Assessment in Neuropsychiatry (SCAN) (Wing et al., 1990) are based on a semi-structured interview, and are increasingly used in epidemiological research studies (e.g., Ayuso-Mateos et al., 2001; Bebbington et al., 1997; McConnell et al., 2002; Meltzer et al., 1995). SCAN has good interrater reliability despite its semi-structured format.

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