Concurrent and Construct Validity of the Outcome Questionnaire

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Abstract
The Outcome Questionnaire (OQ) was developed by Lambert and colleagues (1994) as a standardized measure for assessing psychotherapy outcome. Although the instrument is already being widely used in managed health care quality control, further evidence of its psychometric properties is needed. This research evaluated the concurrent and construct validity of the OQ with three patient samples and a sample of community participants. Support was found for the construct and concurrent validity of the OQ with both patients (n = 183) and nonpatients (n = 210). The data show significant differences in scores between patients and community samples, as well as differences between the various clinical samples with varying levels of pathology. Although high correlations between the OQ Total (and subscale) scores and the criterion measures were found, high intercorrelations among subscales suggest considerable shared variance between subscales. The OQ Total score appears promising as a measure of general psychological distress, although further research is needed to justify the interpretation of subscale scores in clinical settings.