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A set of 15 self-administered case histories were developed, each consisting of a short case followed by a standard format on which desired tests were checked. After pilot testing the case histories within a group of doctors, the authors selected the ten cases with the highest item-total correlations that also provided a broad clinical spectrum. Using a different group of 19 doctors, test-ordering on the questionnaire was compared with actual test-ordering in clinical practice. Questionnaire test-ordering did not reflect practice behavior; in fact, the relationship tended to be inverse (r = -0.43: P less than 0.10). Adjusting for case-mix variation by including only those practice cases with diagnoses similar to questionnaire cases did not improve its performance (r = -0.50: P less than 0.05). These findings suggest that test-ordering on case history questionnaires may not reflect actual practice behavior. Conclusions about test-ordering behavior and management strategies to alter it should not be based on results from questionnaires that have not been validated against actual practice.
Hartley et al. (Tue,) studied this question.