PHQ-9 Calculator

The Patient Health Questionnaire-9 (PHQ-9) is a nine-item self-report measure designed to assess the severity of depressive symptoms over the preceding two weeks. Developed by Drs Robert L. Spitzer, Janet B.W. Williams, and Kurt Kroenke, the PHQ-9 is derived from the larger Patient Health Questionnaire and maps directly onto the nine diagnostic criteria for major depressive disorder in the DSM-IV and DSM-5.

Each item is scored from 0 ("Not at all") to 3 ("Nearly every day"), yielding a total score between 0 and 27. The PHQ-9 is one of the most widely used depression screening instruments globally, with translations available in numerous languages. It is freely available in the public domain, requiring no licensing fees or permissions to use.

The PHQ-9 was developed as part of the PRIME-MD (Primary Care Evaluation of Mental Disorders) project, initially published by Kroenke, Spitzer, and Williams in the Journal of General Internal Medicine in 2001. The original validation study involved 6,000 patients across eight primary care and seven obstetrics clinics.

The instrument demonstrated excellent internal consistency (Cronbach's alpha of 0.89) and strong test-retest reliability (intraclass correlation of 0.84). Construct validity was supported by significant associations with functional impairment, disability days, and healthcare utilisation. As PHQ-9 severity increased, functional status decreased substantially.

Subsequent validation studies across diverse populations — including adolescents, older adults, perinatal women, and culturally diverse groups — have consistently supported the psychometric properties of the PHQ-9. A 2019 individual participant data meta-analysis published in the BMJ by Levis, Benedetti, and Thombs, analysing data from 44 studies and over 58,000 participants, confirmed a pooled sensitivity of 0.88 and specificity of 0.85 at a cut-off score of 10.

The PHQ-9 uses a simple additive scoring model. Each of the nine items is rated on a four-point Likert scale:

0 = Not at all 1 = Several days 2 = More than half the days 3 = Nearly every day

Total scores range from 0 to 27. Published severity thresholds are:

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

A score of 10 or above is commonly used as the threshold for further clinical evaluation. Item 9 ("Thoughts that you would be better off dead, or of hurting yourself in some way") warrants careful attention regardless of the total score, as any positive response may indicate risk that should be explored by a qualified practitioner.

The PHQ-9 serves multiple functions in clinical practice. It is used as a screening tool to identify individuals who may benefit from further assessment, as a severity measure to quantify the degree of depressive symptoms, and as a monitoring tool to track changes over time during the course of care.

The instrument's brevity (typically completed in under three minutes) and its strong psychometric properties make it suitable for routine use in primary care, mental health, hospital, and community settings. Many clinical guidelines recommend its use as part of structured outcome monitoring.

Beyond individual clinical use, the PHQ-9 is widely employed in population health surveys, quality improvement programs, and research studies. Its standardised scoring facilitates meaningful comparisons across settings and over time.

In Australia, the PHQ-9 is widely used across primary care, psychology, psychiatry, and allied health settings. It is referenced in clinical guidelines published by the Royal Australian and New Zealand College of Psychiatrists (RANZCP) and is a recommended outcome measure under the Better Access to Mental Health Care initiative.

For practitioners providing services under Medicare's Better Access program, routine outcome measurement using validated instruments like the PHQ-9 supports evidence-based practice and clinical governance requirements. The PHQ-9 is also used extensively in Australian clinical research and quality improvement studies.

Australian community reference data come from Stocker and colleagues' national survey of 13,829 Australian adults during the COVID-19 period (Psychiatry Research, 2021), and from the Personality and Total Health (PATH) Through Life longitudinal cohort. Both support the standard 5/10/15/20 severity thresholds in Australian populations.

For Aboriginal and Torres Strait Islander people, Brown, Mentha, Rowley and colleagues (2013) developed an adapted PHQ-9 in Aboriginal men in central Australia. The adapted PHQ-9 retains the cut-point of ≥10 for probable depression and provides a culturally informed alternative where appropriate.