The Patient Health Questionnaire-9 (PHQ-9) is a widely used tool for assessing the severity of depression. It consists of nine questions that focus on the symptoms of depression experienced over the past two weeks. Each question is scored from 0 to 3, allowing healthcare providers to quantify the level of depressive symptoms and monitor changes over time. The PHQ-9 is often used in clinical settings, such as hospitals and primary care offices, to help diagnose depression and guide treatment decisions. It is a self-administered questionnaire, making it easy for patients to complete and for providers to interpret the results efficiently.