Clinical Overview
The Patient Health Questionnaire (PHQ-9) is a widely-used 9-item self-administered depression screening and severity assessment tool developed by Dr. Kurt Kroenke and colleagues. Based directly on the nine DSM-5 criteria for major depressive disorder, this validated instrument serves as both a diagnostic aid and a measure of depression severity in primary care and specialty mental health settings. The PHQ-9 evaluates the frequency of depressive symptoms over the past two weeks using a 4-point scale ranging from “not at all” to “nearly every day.” Each item corresponds to a specific DSM-5 criterion for major depression, including depressed mood, anhedonia, sleep disturbances, fatigue, appetite changes, feelings of worthlessness, concentration difficulties, psychomotor symptoms, and suicidal ideation. The scale generates both categorical diagnostic information and dimensional severity scores, making it an essential tool for depression screening, diagnosis, and treatment monitoring across diverse healthcare settings.
Key Validation Points
- Excellent Diagnostic Accuracy – Demonstrated sensitivity of 88% and specificity of 88% for major depressive disorder at cut-off score ≥10
- Strong Psychometric Properties – Robust internal consistency (Cronbach’s alpha 0.86-0.89) and test-retest reliability across diverse populations
- Extensive Validation – Validated across primary care, obstetrical clinics, and specialty mental health settings with established psychometric properties
- Cross-Cultural Validation – Successfully translated and validated in over 30 languages with established measurement invariance across cultural populations
- Treatment Sensitivity – Proven responsiveness to antidepressant medications and psychotherapy with ability to detect clinically meaningful changes
- Healthcare Integration – Widely adopted in healthcare systems worldwide with extensive evidence supporting its clinical utility and cost-effectiveness
Primary Use Cases
- Depression Screening and Diagnosis – Primary screening tool for major depressive disorder with established diagnostic algorithms based on DSM-5 criteria
- Depression Severity Assessment – Dimensional measurement of depression severity with validated cut-off points for mild, moderate, moderately severe, and severe depression
- Treatment Response Monitoring – Longitudinal assessment of symptom changes following antidepressant treatment or psychotherapy interventions
- Primary Care Integration – Efficient screening and monitoring tool widely implemented in primary care and integrated healthcare settings
- Clinical Research Applications – Validated outcome measure for depression research studies and pharmaceutical clinical trials
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