The 9-question Patient Health Questionnaire (PHQ-9) is a diagnostic tool introduced in 2001 to screen adult patients in a primary care setting for the presence and severity of depression. It rates depression based on the self-administered Patient Health Questionnaire (PHQ). The PHQ is part of Pfizer's larger suite of trademarked products, called the Primary Care Evaluation of Mental Disorders (PRIME-MD). The PHQ-9 takes less than 3 minutes to complete and simply scores each of the 9 DSM-IV criteria for depression based on the mood module from the original PRIME-MD. Primary care providers frequently use the PHQ-9 to screen for depression in patients. Source: Wikipedia (en)