The Science Behind Our Depression Quiz

The Instrument: PHQ-9

Our depression quiz is based on the Patient Health Questionnaire-9 (PHQ-9), developed by Kroenke, Spitzer, and Williams in 2001.

What It Measures

The PHQ-9 assesses the nine DSM criteria for major depressive disorder over the past two weeks:

• Little interest or pleasure in doing things (anhedonia)
• Feeling down, depressed, or hopeless
• Trouble falling or staying asleep, or sleeping too much
• Feeling tired or having little energy
• Poor appetite or overeating
• Feeling bad about yourself or that you're a failure
• Trouble concentrating on things
• Moving or speaking noticeably slowly or being fidgety/restless
• Thoughts of self-harm or being better off dead

Severity Levels

PHQ-9 scores are interpreted as follows:

• 0-4: Minimal or no depression
• 5-9: Mild depression
• 10-14: Moderate depression
• 15-19: Moderately severe depression
• 20-27: Severe depression

Validation & Reliability

The PHQ-9 is one of the most validated depression measures in the world:

• Sensitivity: 88% at cutoff score of 10
• Specificity: 88% at cutoff score of 10
• Internal Consistency: Cronbach's alpha of .89
• Test-Retest Reliability: Excellent stability over short intervals
• Validation Sample: Over 6,000 patients across 8 primary care clinics

The PHQ-9 has been translated into over 80 languages and is used in clinical practice, research, and public health globally.

Academic Citations

1. Kroenke, K., Spitzer, R. L., & Williams, J. B. (2001). The PHQ-9: Validity of a brief depression severity measure. Journal of General Internal Medicine, 16(9), 606-613. https://doi.org/10.1046/j.1525-1497.2001.016009606.x
2. Lowe, B., Kroenke, K., Herzog, W., & Grafe, K. (2004). Measuring depression outcome with a brief self-report instrument: Sensitivity to change of the Patient Health Questionnaire (PHQ-9). Journal of Affective Disorders, 81(1), 61-66. https://doi.org/10.1016/S0165-0327(03)00198-8
3. Gilbody, S., Richards, D., Brealey, S., & Hewitt, C. (2007). Screening for depression in medical settings with the Patient Health Questionnaire (PHQ): A diagnostic meta-analysis. Journal of General Internal Medicine, 22(11), 1596-1602. https://doi.org/10.1007/s11606-007-0333-y
4. American Psychiatric Association. (2013). Diagnostic and statistical manual of mental disorders (5th ed.). American Psychiatric Publishing.
5. Cuijpers, P., Quero, S., Dowrick, C., & Arroll, B. (2019). Psychological treatment of depression in primary care: Recent developments. Current Psychiatry Reports, 21(12), 129. https://doi.org/10.1007/s11920-019-1117-x

Limitations

While the PHQ-9 is highly validated, it has important limitations:

• Screening, Not Diagnosis: A positive screen requires clinical evaluation for diagnosis
• Self-Report Bias: Results depend on honest self-assessment
• Symptom Overlap: Depression symptoms can overlap with medical conditions, grief, and other psychiatric disorders
• Cultural Considerations: Depression expression varies across cultures

Clinical diagnosis of depression requires comprehensive evaluation by a qualified mental health professional.