An illustration of how a self-report diagnostic screening scale could improve the internal validity of antidepressant efficacy trials

Background: During the past 20 years semi-structured diagnostic interviews have been the standard for diagnostic evaluations in research relying on reliable and valid psychiatric assessment and diagnosis; however, only a minority of antidepressant efficacy trials (AETs) employ these interviews. This might be important insofar as several studies have found that clinicians conducting unstructured clinical interviews underrecognize diagnostic comorbidity. Because of the financial incentives to recruit patients into AETs quickly, there is little incentive to vigorously determine the presence of comorbid conditions that should result in exclusion from the trial. In the present report we demonstrate how a self-report diagnostic screening scale could be used to identify systematic differences in diagnostic practice across settings, and how such a scale could be used to compare samples of patients who pass screening evaluations and are accepted into an AET. Methods: Depressed patients completed the Psychiatric Diagnostic Screening Questionnaire (PDSQ), and were evaluated with either an unstructured clinical interview or with the Structured Clinical Interview for DSM-IV (SCID). Results: The two samples were clinically comparable based on their scores on the self-administered PDSQ. Consistent with the greater thoroughness of the SCID, compared to unstructured diagnostic evaluations, more patients administered the SCID were diagnosed with comorbid conditions. After excluding patients with disorders that might be the basis for exclusion from an AET, the two samples then differed in their scores on the PDSQ. That is, more patients in the sample evaluated by an unstructured interview had ‘occult’ pathology than patients evaluated with the SCID. Conclusion: These findings demonstrate how systematic differences in diagnostic practice might be detected across sites when conducting AETs. Limitations: The study was conducted with patients in a single outpatient clinical practice rather than participants of a multi-site trial.