Depression rates around the world vary according to a nation\'s affluence, with the high income countries -- including the U.S. -- reporting the higher levels of depression, a study published in the journal BMC Medicine shows. An international team of researchers collected the results of face-to-face interviews of nearly 90,000 people considered representatives of their population. The interviews were conducted in community settings in 18 countries, and the interviewers used a standard diagnostic test from the World Health Organization (WHO) to assess depression. In the 10 countries considered high-income, an average of 15 percent of participants said they’d experienced a depressive episode in their lifetime. France, the Netherlands, New Zealand and the U.S. all had rates higher than 18 percent. But among the eight low- to middle-income countries surveyed, the rate was 11 percent -- the lowest rates were found in India, Mexico, China and South Africa. The authors acknowledged that language barriers, difficulty in recalling the past and reluctance to be open with a foreign interviewer make it difficult to directly compare results between countries. Nevertheless they speculated that perhaps rich nations have more stressful environments, or that the gap between rich and poor is large in affluent countries, which would induce depression. They concluded that more research is needed into the social conditions that are related to depression