This document discusses depression, including statistics on prevalence, symptoms, classification of severity, and potential causes and treatments. Some key points: - Around 5% of the world population suffers from depression, including 5% of those over age 60. - Main symptoms include depressed mood, loss of interest, fatigue, and difficulty concentrating. - Severity is classified as mild, moderate, or major depending on number of core and additional symptoms. - Potential causes include childhood adversity, medical conditions and treatments, and other diseases. - Treatments discussed include psychotherapy, medication, electroconvulsive therapy, light therapy, and social support.