Congrats, America, You Lead the World in Mental Illness 6.75K Brian Moylan 03/11/11 03:50PM Filed to: Studies Studies Bipolar Manic depression Science shutterstock A study of bipolar disorder (sometimes called manic depression) in 11 countries showed that the highest percentage of bipolar people (4.4% of the population) are here in the U.S. of A. We don't know whether to be excited or sad.