The Patient Health Questionnaire (PHQ) is a multi-purpose tool for screening, diagnosing, monitoring, and measuring the severity of depression. The PHQ tool rates the frequency of symptoms, which is then used as a factor in the scoring severity index. The PHQ-9 and PHQ-2, components of the longer Patient Health Questionnaire, offer psychologists concise, self-administered tools for assessing depression. The PHQ incorporates the DSM-IV depression criteria with other leading major depressive symptoms into a brief self-report instruments. The sensitivity of PHQ-9 scores > 10 is 88% and a specificity of 88% for Major Depressive Disorder. The reliability and validity of the tool has prooved to contain sound psychometric properties. The PHQ-9 also has a high internal consistency.

Pfizer holds the copyright to the PHQ-9, but is available for use and replication without needing permission to be granted. The number 9 in PHQ-9 is a reference to the nine questions to assess each criterion of depression according to the Diagnostic and Statistical Manual of Mental Disorders. The PHQ-9 is commonly administered in doctor’s or therapist’s offices as a part of routine checkups, or as a way to monitor and evaluate a patient’s mental health. The higher the score, the more symptoms of depression one experiences, and the more severe their depression is.

The  PHQ-2 contains the first 2 items of the PHQ-9 and enquires about the degree to which an individual has experienced depressed mood and anhedonia over the past two weeks. The primary gaol of the PHQ-9 is not to monitor depression severity but to screen for depression. Patients with positive screening results should be further evaluated with the PHQ-9 to determine whether they meet criteria for a depressive disorder. The PHQ-2 has been validated in 3 studies in which it showed wide variability in sensitivity. It is free & available in over 30 languages.