PHQ-9 and GAD-7 are the two most widely validated self-report screening tools for depression and anxiety disorders in primary care and mental health settings. The Patient Health Questionnaire-9 (PHQ-9) contains nine items directly corresponding to DSM-5 criteria for major depressive disorder, assessing symptoms such as low mood, anhedonia (loss of interest), sleep and appetite changes, worthlessness, and concentration difficulties over the preceding two weeks. The Generalised Anxiety Disorder-7 (GAD-7) similarly evaluates seven core anxiety symptoms—including nervousness, uncontrollable worry, restlessness, irritability, and somatic tension—over the same two-week period. Both instruments employ a 4-point Likert scale (0 = “not at all” to 3 = “nearly every day”), with total scores ranging from 0 to 21 for the GAD-7 and 0 to 27 for the PHQ-9.
Psychometric Data
- PHQ-9 (cut-off ≥10): Sensitivity 86%, Specificity 83% for major depression
- GAD-7 (cut-off ≥7): Sensitivity 75%, Specificity 80% for generalized anxiety
- GAD-7 (cut-off ≥10): Sensitivity 55%, Specificity 89%
- Combined PHQ-9 + GAD-7: Higher diagnostic accuracy (AUC = 0.882) vs. PHQ-9 alone (AUC = 0.800) or GAD-7 alone (AUC = 0.830)
- Negative likelihood ratios (<0.1): Both tools demonstrate excellent ability to exclude depression and anxiety when scores are low
Severity Thresholds
- PHQ-9: 0-4 normal, 5-9 mild, 10-14 moderate, 15-19 moderately severe, 20-27 severe
- GAD-7: 0-4 normal, 5-9 mild, 10-14 moderate, 15-21 severe (cut-off ≥7 indicates “caseness”)
Clinical Applications
- Internal consistency: Cronbach’s alpha 0.80-0.89 for both tools
- Strong criterion validity across diverse populations, including low- and middle-income countries
- Ultra-brief versions (PHQ-2, GAD-2) correlate strongly with full versions but omit somatic symptom items (particularly relevant for young people)
- Network analysis confirms close links between PHQ-9 and GAD-7 items—worry and nervousness link to depressed mood and anhedonia
The PHQ-9 and GAD-7 are screening tools, not diagnostic instruments—they provide quantitative severity metrics that facilitate evidence-based clinical decision-making but do not substitute for comprehensive psychiatric evaluation. With strong psychometric properties, established cut-offs, and demonstrated utility across primary care, mental health, and research settings, these complementary measures offer a time-efficient, validated approach to identifying and monitoring depression and anxiety—two conditions that frequently co-occur and together affect hundreds of millions worldwide.
