PHQ9

The PHQ-9, or Patient Health Questionnaire-9, is a self-administered instrument used to screen for, diagnose, and monitor depressive symptoms. It is based on the diagnostic criteria for major depressive disorder in the DSM and consists of nine questions that reflect those criteria.

Each item asks about the frequency of a symptom over the past two weeks, with response options scored as 0 for "not at all," 1 for "several days," 2 for "more than half the days," and 3 for "nearly every day." The total score ranges from 0 to 27. Scores are commonly interpreted as follows: 0–4 minimal, 5–9 mild, 10–14 moderate, 15–19 moderately severe, and 20–27 severe depressive symptoms. A score of 10 or higher is often used as a threshold indicating clinically significant depressive symptoms and may warrant further assessment.

The PHQ-9 serves multiple clinical and research roles, including screening in primary care, aiding diagnostic assessment, and monitoring symptom change during treatment. It is frequently used to track response to therapy over time and to inform treatment decisions.

Item 9 asks about thoughts of being better off dead or self-harm and is intended to screen for suicidality. A positive response to this item requires immediate follow-up with risk assessment and safety planning according to clinical guidelines.

Limitations include its nature as a self-report measure, which may be influenced by reporting biases and cultural or linguistic factors. It is not a substitute for a full clinical interview and should be interpreted within the broader clinical context. The PHQ-9 is widely used and freely available for clinical and research purposes.