The BDI, or Beck Depression Inventory, is a widely used self-report questionnaire designed to assess the severity of depression in individuals. Developed by Dr. Aaron T. Beck in the 1960s, it consists of 21 multiple-choice questions that cover various symptoms of depression, such as sadness, hopelessness, and changes in sleep patterns. Each item is scored on a scale, allowing healthcare professionals to gauge the intensity of a person's depressive symptoms. The BDI is commonly used in clinical settings and research to help diagnose depression and monitor treatment progress. It is suitable for adolescents and adults, making it a versatile tool in mental health assessments. The results can guide therapists and doctors in creating effective treatment plans tailored to the individual's needs.