Rates and ranking among all causes of disability varied by country and by region. The rates are highest in Afghanistan and lowest in Japan, and depression ranks first in Central America and Central and Southeast Asia. Disability from depression affects mostly people in their working years, and women more than men.
To arrive at the estimates, the authors of the study, led by Alize Ferrari from the University of Queensland and the Queensland Centre for Mental Health Research, compiled relevant information from all published research studies on major depressive disorder (MDD, also called clinical depression), and dysthymia, a milder chronic form of depression.
They then used mathematical tools to estimate a standard measure of disease burden: "disability-adjusted life years", or DALYs, calculated by adding together "years lived with a disability", or YLDs and "years lost because of disease-specific premature death" or YLLs. For some countries and regions, especially low-income countries, few studies had been published, and the researchers had to substitute actual numbers with reasonable estimates to calculate YLDs and DALYs.
When compared to other diseases and injuries, MDD ranked as the second leading cause of global disability (or YLDs) and eleventh leading cause of global burden (or DALYs) in 2010. However, MDD also contributes to mortality for a number of other conditions. When the researchers added DALYs attributable to MDD for two of them, namely suicide and ischemic heart disease, MDD ranked as the eighth leading cause of global burden.
Their results, the researchers say "not only highlight the fact that depressive disorders are a global health priority but also that it is important to understand variations in burden by disorder, country, region, age, sex, and year when setting global health objectives."