According to WebMD:
The CDC says that about 9% of Americans report they are depressed at least occasionally, and 3.4% suffer from major depression.
The 9% are people who reported to surveyors that they felt depressed to some degree in the two weeks prior to being questioned. That includes the 3.4% of adults who meet the CDC’s criteria for major depression.
The analysis, part of the CDC’s Morbidity and Mortality Weekly Report(MMWR) for Oct. 1, was based on a survey of 235,067 people aged 18 and older in 45 states, Washington, D.C., Puerto Rico, and the Virgin Islands.
According to the MMWR, estimates for current depression in states and territories in 2006-2008 ranged from a low of 4.8% in North Dakota to 14.8% in Mississippi. People in Kentucky, New Jersey, North Carolina, Pennsylvania, and South Dakota did not participate in either the 2006 or the 2008 survey.
340 million people in the world suffer from depression and rising
1 in 4 women will suffer from depression
1 in 10 men will suffer from depression (this statistic is not absolutely correct because more women are apt to see their doctor for depression than men do.)
Depression strikes all races, rich and poor.
Read more: http://wiki.answers.com/Q/How_many_people_in_the_world_suffer_from_depression#ixzz2J6DEV02m