Mental disorders from severe depression to uncontrolled anger are surprisingly common around the world, and most of the worst cases are not being treated, researchers reported on Tuesday.

The biggest concerted study of global mental illness shows that rates vary greatly - with 4.3 percent of people living in Shanghai showing symptoms of mental disorders in the past year, compared to 26 percent in the United States.

Even if people are not concealing their histories of mental illness - which many undoubtedly are - the problem is enormous, said Ronald Kessler of Harvard Medical School in Boston, who led the World Health Organization study.

His team’s study, published in the Journal of the American Medical Association, shows that many people with severe mental disorders are getting no treatment at all, while many others with only mild problems are being treated.

“It is clear from these results that there is undertreatment of serious disorders,” Kessler told a news conference.

More than 60 percent of people who had serious mental disorders in Spain and France had been treated, and about 50 percent in Belgium the United States, Netherlands and Germany.

But fewer than 20 percent of patients with serious mental illness in Colombia, Mexico, Ukraine and Lebanon had been treated.

In the United States, more rich, suburban patients are being treated for mild mental illnesses than are poor people with serious mental illness, Kessler said.

And 35 percent of Spaniards with mild mental disorders reported getting treatment and more than 25 percent in Belgium, Germany and the Netherlands.

Kessler’s team includes 100 experts aided by 3,000 interviewers, who are surveying more than 60,000 adults in 14 countries. They include psychiatrists trained to find concealed symptoms of mental illness.

People in some countries were much more likely to report mental disorders such as obsessive compulsive disorder, bulimia, or post traumatic stress disorder, Kessler said.

“We always find rates are highest in the United States. Whether that is true or whether people are more willing to admit it in the United States we don’t know,” Kessler said.

Those interviewed in Japan reported a 5 percent rate of anxiety disorders, for instance, and in China less than 4 percent. This compares to more than 18 percent in the United States.

But Kessler said reported rates in Japan and China were “implausibly low,” as Japan has the world’s highest use of anti-anxiety drugs called benzodiazepines and China has the world’s highest rate of suicide.