Patient Health Questionnaire-9: A clinimetric analysis

Objective: The Patient Health Questionnaire-9 (PHQ-9) is a widely used self-reported measure of depression, which was found to display only acceptable psychometric properties. Insufficient attention has been devoted to its clinimetric validity and its clinical utility is still debated, particularly when used for assessing depression severity. This is the first study testing PHQ-9 construct validity and clinical utility based on clinimetric principles. Methods: An online survey involving a sample of 3,398 participants was conducted. Item Response Theory models (Rasch and Mokken analyses) were used to assess PHQ-9 validity and determine its clinical utility. Results: Fit to the Rasch model was achieved after adjusting the sample size. Items 2, 4, 6, 9 displayed over-discrimination, items 1, 5, 7 showed under-discrimination. Indication of local dependency between items 2 and 6 was found. PHQ-9 was not unidimensional. A Loevinger's coefficient of 0.49 was found, indicating an acceptable level of scalability. Conclusions: PHQ-9 is a measure of potential clinical utility to be used as an overall index of depression, mainly for screening purposes. Substantial revisions, particularly in the wording of over- and under-discriminating items, are needed.