Problem: What is the purpose, methods, and finding of this article? Introduction Major depressive disorder (MDD) is one of the most prevalent mental disorders worldwide, as well as one of the most disabling. According to the Global Burden of Disease study, depression is the fourth leading cause of disability (measured in disability adjusted life years), and it is expected to be the second by 2020.1 MDD has a greater impact on public health than physical conditions such as coronary heart disease, rheumatoid arthritis, or diabetes mellitus.2 Its economic impact is also considerable.3-5 Information on the prevalence and correlates of MDD is key to its prevention and management. Since the 1980s, a number of population surveys have explored the prevalence of mental disorders. Some of the first large-scale studies were the Epidemiologic Catchment Area (1980-1985)6 and the National Comorbidity Survey (1990-1992),7 both conducted in the United States. It took several years before such studies were conducted in developing countries. Although a number of surveys have been carried out in recent years, their methodological differences make it difficult to obtain comparable results, even within the same country. This issue has been addressed by the World Health Organization through the World Mental Health project