Patient Health Questionnaire Anxiety and Depression Scale: Initial Validation in Three Clinical Trials

Abstract

OBJECTIVE: We examine the reliability and validity of the Patient Health Questionnaire Anxiety and Depression Scale (PHQ-ADS)-which combines the nine-item Patient Health Questionnaire depression scale and seven-item Generalized Anxiety Disorder scale-as a composite measure of depression and anxiety. METHODS: Baseline data from 896 patients enrolled in two primary-care based trials of chronic pain and one oncology-practice-based trial of depression and pain were analyzed. The internal reliability, standard error of measurement, and convergent, construct, and factor structure validity, as well as sensitivity to change of the PHQ-ADS were examined. RESULTS: The PHQ-ADS demonstrated high internal reliability (Cronbach α values of .8 to .9) in all three trials. PHQ-ADS scores can range from 0 to 48 (with higher scores indicating more severe depression/anxiety), and the estimated standard error of measurement was approximately 3 to 4 points. The PHQ-ADS showed strong convergent (most correlations, 0.7-0.8 range) and construct (most correlations, 0.4-0.6 range) validity when examining its association with other mental health, quality of life, and disability measures. PHQ-ADS cutpoints of 10, 20, and 30 indicated mild, moderate, and severe levels of depression/anxiety, respectively. Bifactor analysis showed sufficient unidimensionality of the PHQ-ADS score. PHQ-ADS change scores at 3 months differentiated (p < .0001) between individuals classified as worse, stable, or improved by a reference measure, providing preliminary evidence for sensitivity to change. CONCLUSIONS: The PHQ-ADS may be a reliable and valid composite measure of depression and anxiety which, if validated in other populations, could be useful as a single measure for jointly assessing two of the most common psychological conditions in clinical practice and research.