Although millions of American adults are affected by major depression each year, only the minority receives proper treatment, according to a 2-year nationwide study published in the June 18th issue of the Journal of the American Medical Association.

The study found high rates of major depressive episodes in all segments of the U.S. population. The researchers measured the severity and duration of depression in more than 9,000 Americans 18 years or older, looked at the effects of major depression on daily activities, and evaluated treatment received, if any.

"This is the first study to assess clinical severity of depression in a community sample," said survey leader Ronald Kessler, professor of health care policy at Harvard Medical School.

"Critics have suggested that depression was overestimated in earlier studies because of many people with mild depression being included even though they really don't need treatment," Kessler said. "But we built in a state-of-the-art clinical severity assessment, and we found that the majority of people with major depressive episodes are severe cases, and only a small minority are mild cases.

“The average person with a major depressive episode in the past year reported an average of 35 days when they were unable to work or carry out other normal activities because of their depression. These findings confirm that depression is an enormous societal problem, both in terms of the number of people involved and in terms of clinical severity."

Although most people reporting depression in the past 12 months received some kind of treatment -- an improvement over findings from earlier studies -- only 1 in 5 received treatment that met minimum standards of treatment adequacy established by the U.S. Agency for Health Care Policy and Research.

The researchers found that inadequate treatment was due to a mix of inappropriate dosing of antidepressant medications on the part of physicians, patient discontinuation of treatment, and use of unproven treatments outside the medical and mental health system.

"While recently increased treatment is encouraging, inadequate treatment is a serious concern," the authors wrote. "Emphasis on screening and expansion of treatment needs to be accompanied by a parallel emphasis on treatment quality improvement."

The study found that women and people previously married were most at risk for major depression over a lifetime; in a 12-month period, major depressive episode was more common among homemakers, people who had never married, and those who had not completed high school or who were living in poverty. Neither geographic region nor urban versus rural residence was closely related to incidence of disease.

The researchers found major depression affects 13 to 14 million American adults--roughly 6.6 percent--in a given year. In a lifetime, 16.2 percent of Americans--about 33 to 35 million?will be affected by major depression.