Patient Health Questionnaire – Depression (PHQ-9)

Abstract

The Patient Health Questionnaire – Depression (PHQ-9) is a concise, nine-item instrument derived from the larger Patient Health Questionnaire (PHQ). It serves as a crucial screening and severity measure for Major Depressive Disorder (MDD) in clinical settings, particularly in primary care. The scale is directly rooted in the diagnostic criteria for MDD outlined in the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV), facilitating its integration into clinical decision-making processes and the monitoring of treatment efficacy.

Keywords

PHQ-9, depression screening, major depressive disorder, primary care, psychometrics, DSM-IV, severity measure, clinical assessment.

Authors

Drs. Robert L. Spitzer, Janet B.W. Williams, Kurt Kroenke.

Purpose

The primary purpose of the PHQ-9 is twofold: to assist primary care clinicians in the rapid identification and provisional diagnosis of major depression, and to monitor patient response to treatment over time. Its brevity and ease of administration make it highly suitable for high-volume clinical environments where time and resources may be limited.

The instrument provides quantified severity scores, allowing practitioners to categorize depression into clinical levels (e.g., mild, moderate, severe). This quantification aids in determining the appropriate level of intervention and tracking improvement or deterioration during follow-up visits, thereby enhancing collaborative care models.

Construct

The PHQ-9 is designed to measure the severity and presence of symptoms aligned with the diagnostic criteria for Major Depressive Disorder (MDD) as defined by the American Psychiatric Association (APA). It specifically assesses the frequency of the nine core symptom clusters required for an MDD diagnosis over the previous two weeks.

The items cover key areas of depressive symptomatology, including anhedonia (loss of interest or pleasure), depressed mood, sleep disturbance, fatigue, changes in appetite, feelings of guilt or worthlessness, concentration difficulties, psychomotor agitation or retardation, and suicidal ideation. The cumulative score reflects the overall burden of depressive symptoms experienced by the individual.

Validity

The validity of the PHQ-9 has been robustly established through large-scale clinical trials. Criterion validity was assessed by comparing PHQ-9 scores against independent structured mental health professional interviews (the gold standard) in a sample of 580 patients. The results demonstrated strong discriminative ability across diagnostic categories.

Specifically, a cutoff score of 10 or greater demonstrated high accuracy for identifying major depression, yielding a sensitivity of 88% and a specificity of 88%. Furthermore, construct validity was supported by the significant differences in mean scores across groups: 17.1 (SD 6.1) for major depression, 10.4 (SD 5.4) for other depressive disorders, and 3.3 (SD 3.8) for non-depressed individuals.

Reliability

The reliability of the PHQ-9, primarily assessed via internal consistency, is consistently reported as high across diverse populations. The initial validation study administered the scale to 6,000 patients across 8 primary care and 7 obstetrics-gynecology clinics, providing a broad empirical foundation for its consistency in varied clinical settings.

Although the original source focuses heavily on validity data, subsequent psychometric literature consistently confirms the strong internal consistency of the scale (typically measured by Cronbach’s alpha exceeding 0.80), indicating that the items reliably cohere to measure the singular construct of depression severity.

Factor Analysis

The PHQ-9 is conceptually designed as a unidimensional instrument, reflecting the cumulative nature of DSM diagnostic criteria for major depression. Initial and subsequent factor analysis studies generally support a robust single-factor solution, confirming its use as a measure of overall depression severity.

However, some research across different cultural or clinical populations has suggested the presence of two correlated factors: a somatic factor (including symptoms like sleep, appetite, and fatigue) and a cognitive-affective factor (including mood, guilt, and suicidal ideation). Despite these minor structural nuances, the PHQ-9 is universally scored as a single, cumulative index ranging from 0 to 27 for clinical interpretation.

Instrument

Test Type: Self-report questionnaire / Clinical diagnostic aid

Format: Nine Likert-scaled items, scored 0 to 3, yielding a total score from 0 to 27. Severity thresholds are defined as: 5-9 (Mild), 10-14 (Moderate), 15-19 (Moderately Severe), and 20-27 (Severe).

Language Available: Widely translated and validated in numerous languages globally, facilitating international research and clinical use.

Population Group: General patient population; primarily utilized in primary care, general medicine, and obstetrics-gynecology settings.

Age Group: Adolescents (typically 13 years and older) and Adults.

Population Details: Initial validation included a large sample of 6,000 patients drawn from outpatient medical clinics.

Test Methodology: Patients rate the frequency with which they have experienced each of the nine problems over the preceding two weeks.

Keywords

Patient Health Questionnaire, depressive symptoms, screening tool, clinical psychology, psychopathology, severity index, primary care screening, mental health assessment.

Authors

Author ORCID Identifier: Not provided in source.

Affiliation Email addresses: Not provided in source.

Correspondence Address: Not provided in source.

Permissions & Fee and Test Year

The PHQ-9 is generally considered to be in the public domain and is available for free, non-commercial use in research and clinical practice. Permission is typically not required for reproduction, provided the scale is not modified. The original publication detailing the development and validation of the PHQ-9 was released in 2001.

Reference’s

• Kroenke, K., Spitzer, R. L., & Williams, J. B. W. (2001). The PHQ‐9. Journal of general internal medicine, 16(9), 606-613.

• The scale is based on the criteria found in the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV).

Items of the Patient Health Questionnaire – Depression (PHQ-9)

IMPORTANT: The following scale items must be preserved in their original language and must not be changed in any way.

Instructions: Over the last 2 weeks, how often have you been bothered by any of the following problems?

The items are scored on a 4-point scale:

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