Patient Health Questionnaire–9 (PHQ-9)

Foundational Context

The PHQ-9 was developed as part of the Patient Health Questionnaire suite to provide a brief yet clinically robust measure of depression severity. Prior depression scales were often long or specialized, making them impractical for routine use. The PHQ-9’s direct correspondence to DSM diagnostic criteria allows clinicians to rapidly identify symptoms consistent with major depressive disorder while also capturing functional impact.

Kroenke et al. (2001) demonstrated that the PHQ-9 has strong psychometric properties, performs well in diagnosing probable depression, and is sensitive to clinical change across a variety of settings. Its accessibility and ease of interpretation have contributed to widespread adoption across primary care, mental health, telehealth, research, and integrated behavioral health environments.

What the Assessment Measures

The PHQ-9 captures symptoms of depression experienced over the past two weeks, including:

• Low mood or anhedonia
• Changes in appetite or sleep
• Fatigue and low energy
• Feelings of worthlessness or guilt
• Poor concentration
• Psychomotor changes
• Thoughts of death or self-harm (Item 9)

The scale reflects symptom frequency and functional impact, supporting both screening and treatment planning.

Interpretation Guidelines

The PHQ-9 produces a total score between 0–27, reflecting depression severity.

Validated severity thresholds:

• 0–4: Minimal depression
• 5–9: Mild depression
• 10–14: Moderate depression
• 15–19: Moderately severe depression
• 20–27: Severe depression

Clinical threshold:

• ≥10 is the standard cutoff for clinically significant depression and warrants further clinical assessment.

Item 9 (Suicidal Ideation):

• Any score >0 requires immediate clinical follow-up.
• Item 9 does not establish risk level alone but signals the need for safety assessment, context gathering, and clinical judgment.

Interpretation Notes:

• The PHQ-9 is a severity measure, not a stand-alone diagnostic tool.
• High scores should be evaluated alongside functional impairment, medical history, and contextual stressors.
• Somatic symptoms may overlap with chronic illness, sleep disorders, or stress responses.
• Must be interpreted within cultural, developmental, and gender-related considerations.
• Rapid increases in score should prompt clinical review.

Psychometric Properties

Reliability

• Excellent internal consistency (α ≈ .89)
• Strong test–retest reliability across clinical and community settings

Validity

• High sensitivity and specificity for major depressive disorder at the ≥10 cutoff
• Strong correlation with clinician-administered diagnostic interviews
• Responsive to treatment-related change
• Valid across primary care, psychiatric, and general population samples

Administration Considerations

• Ideal for both screening and ongoing symptom monitoring
• Works well alongside the GAD-7 for integrated mood/anxiety assessment
• Can be administered verbally, on paper, or digitally
• Should be paired with follow-up assessment when Item 9 is positive
• Functional impairment questions (often included as an add-on) strengthen diagnostic clarity

Limitations

• Does not differentiate between depressive subtypes
• Somatic symptoms may inflate scores for individuals with chronic medical conditions
• Self-report may be influenced by stigma, insight, or response bias
• Not sufficient alone for diagnosing major depressive disorder