Questionnaires And Interviews

If, as I have argued, there are doubts in principle about the validity of structured questionnaires, it is worth knowing how their performance compares with semi-standardized interviews. One head-to-head comparison has been made between SCAN and CIDI (Brugha et al., 2001). This permits two separate questions:

(1) Does the questionnaire provide a similar frequency of disorder to that established by the semi-structured interview?

(2) To what extent are the same cases identified by the two instruments?

Differences in frequencies would, at the very least, indicate some systematic biases separating the instruments. However, even if, for example, CIDI recognized more cases than SCAN, it could still be the case that CIDI picked up most or all of the cases identified by SCAN. This would imply that the constraints of a rigid questionnaire tended to lower the threshold of case identification, as might be the case if the rigidity and the paucity of elaborative questions led to over-recognition of specific symptoms. If, however, in addition to over-recognition of cases, there were little overlap between the cases found by the two systems, this would indicate a more general failure of rigid questioning to establish symptoms properly.

Brugha and his colleagues (2001) conducted a two-phase study of the general population of Leicestershire, UK. In the second phase, 172 subjects selected for an increased probability of exhibiting cases of psychiatric disorder were interviewed with both CIDI and SCAN, in random order. The coefficients of concordance for the various ICD-10 diagnoses varied between poor and fair. The authors calculated that using CIDI would give prevalences about 50% greater than those obtained from SCAN. The index of agreement for any depressive episode was poor (0.14). As expected, the discrepancies arose particularly from cases around the threshold for recognition.

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