Depression is widespread globally, according to a new survey based on interviews with 89,000 people in 18 countries .
They included higher-income countries like Spain, Japan and the United States and low-to-middle income ones such as India, Lebanon and Ukraine.
In the high-income countries, 15 percent had at least one episode of major depression over their lifetime. In lower-income nations, the rate was somewhat lower, about 11 percent.
The study was carried out in conjunction with the World Health Organization's Mental Health Survey Initiative.
"Major depression is defined as a period where you have a number of symptoms of depression that go on all day long, every day, for at least a two-week period," says Evelyn Bromet of the State University of New York, who co-authored a paper describing the findings.
Those symptoms include loss of appetite, trouble concentrating and disturbed sleep patterns, all the way to attempted suicide.
In addition to the broadly similar rates of depression, this international survey found other similarities, too.
"Women were much more likely to have periods of depression than men, everywhere," she says. "And people who were separated or divorced were much more likely to have depression in the last year than other people."
One difference researchers found had to do with age. In the United States and western Europe, rates of depression are highest among younger people.
"But when we did the survey in Ukraine and some of the other poorer countries, we found the opposite - that older people were more likely to have periods of depression in the last 12 months than younger people."
Bromet, who led the survey team in Ukraine, she says the higher rates of depression there may be related to older adults' difficulty in adjusting to the changes in the post-communist world.