Scientific background: Depression
About this test
The PHQ-9 was developed by Spitzer, Kroenke, and Williams (1999) based on the DSM-IV criteria for major depression and is one of the most extensively studied screening instruments in clinical psychology and primary care. Numerous studies show good internal consistency (Cronbach's alpha usually above .85) as well as good sensitivity and specificity for detecting depressive disorders. The PHQ-9 is a screening and monitoring tool, not a diagnosis by itself — that always requires a clinical conversation.
The original study included 6,000 patients across eight primary care and seven obstetrics-gynecology clinics; criterion validity was additionally checked in 580 people against an independent structured interview by a mental health professional. At the cutoff of 10 points, the PHQ-9 reached a sensitivity of 88% and a specificity of 88% for detecting major depression -- a well-balanced trade-off between missed cases and false alarms.
Dimensions
Depression severity (total score)
Sum across all nine symptom items (0–27 points).
Sources & license
Kroenke, K., Spitzer, R. L., & Williams, J. B. W. (2001). The PHQ-9: Validity of a brief depression severity measure. Journal of General Internal Medicine, 16(9), 606–613.
The PHQ-9 is in the public domain and may be reproduced, translated, and used without permission.
https://www.phqscreeners.com
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