This easy to use Patient Health Questionnaire or PHQ-9 is a self-administered instrument for common mental disorders, a depression module, which scores each of the nine DSM-IV criteria as "0" (not at all) to "3" (nearly every day). 

PHQ-9 is not a screening tool for depression but it is used to monitor the severity of depression and response to treatment and it can also be used to make a tentative diagnosis of depression in at-risk populations.

When screening for depression the Patient Health Questionnaire (PHQ-2) can be used first (it has a 97% sensitivity and a 67% specificity).If this is positive, the PHQ-9 can then be used, which has 61% sensitivity and 94% specificity in adults.

The Patient Health Questionnaire (PHQ-2) is a 2-questions short screening test that asks you about your depressed moods and/or inability to feel pressure over the last 2 weeks. The purpose of the PHQ-2 is not to establish a final diagnosis but it should be used as a "first step", a screening test to screen for depression. People screening positive on the PHQ-2, those with an elevated score should see a doctor or do the PHQ-9 9-question test to assess if they meet criteria for a depressive disorder. 

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