Occurrence
The lifetime risk for major depressive disorder has varied across research studies from 10% to 25% for women and 5% to 12% for men. These rates appear to be unrelated to ethnicity, education, income, or marital status. Major depressive disorder may begin at any age, but the average age of onset appears to be mid-twenties. It is twice as common in adolescent and adult females as it is in adolescent and adult males. In children, boys and girls are equally affected.