[1][2][3] The PHQ-9 is a component of the larger self-administered Patient Health Questionnaire (PHQ), but can be used as a stand-alone instrument.
[4] The PHQ is part of Pfizer's larger suite of trademarked products, called the Primary Care Evaluation of Mental Disorders (PRIME-MD).
The PHQ is a self-administered version of the PRIME-MD, a screening tool that assesses 12 mental and emotional health disorders.
The PHQ-9 questions reflect the diagnostic criteria for major depressive disorder (MDD) found in the DSM-5.
[3] A tenth question asks about the extent to which the previously mentioned symptoms make functioning in daily life difficult.
[4] A massive study of almost 60,000 participants (involving 29 samples from seven countries and speaking five languages) that employed exploratory structural equation modeling bifactor analysis showed the PHQ-9 is essentially unidimensional; cognitive-affective and somatic specific factors were relatively weak.
For example, a trained clinician can determine if the symptoms can be better explained by substance use or another medical or psychiatric condition.
[10] By contrast, the results of the massive study by Bianchi et al. (2022)[9] indicate that the PHQ-9's total score is essentially unidimensional.
[1][10][9] In an assessment of construct validity, Kroenke et al.[1] found that the correlation between the PHQ-9 and the SF-20 mental health scale was 0.73.
[1] Preliminary work using gold standard readability measures suggests that a significant minority of patients might find interpretation of the PHQ-9 difficult without support.
[11] The National Institute for Health and Clinical Excellence endorsed the PHQ-9 for measuring depression severity and responsiveness to treatment in adults in a primary care setting.
The Veterans Administration, Department of Defense, and Kaiser Permanente adopted the PHQ-9 as a standard measure for depression screening.
[14] Researchers have used the PHQ-9 to study the mental health of patients with diabetes,[15] HIV-AIDS,[16] chronic pain, arthritis, fibromyalgia, epilepsy, and substance abuse.
The 8-item version of the instrument is commonly used in research on general population samples, which mostly comprises individuals who are not depressed.
A total score that is greater than 3 indicates that a clinician should administer the full GAD-7 and conduct a clinical interview to assess the presence and type of anxiety disorder.