Chicago ? To you, that angry, horn-blasting tailgater is suffering from road rage. But doctors have another name for it – intermittent explosive disorder – and a new study suggests it is far more common than they realized, affecting up to 16 million Americans, or one person in 20.

“People think it’s bad behavior and that you just need an attitude adjustment, but what they don’t know … is that there’s a biology and cognitive science to this,” said Dr. Emil Coccaro, chairman of psychiatry at the University of Chicago’s medical school.

Road rage, temper outbursts that involve throwing or breaking objects and even spousal abuse can sometimes be attributed to the disorder, though not everyone who does those things is afflicted.

By definition, intermittent explosive disorder involves multiple outbursts that are way out of proportion to the situation. These angry outbursts often include threats or aggressive actions and property damage. The disorder typically first appears in adolescence; in the study, the average age of onset was 14.

The study was based on a national face-to-face survey of 9,282 U.S. adults who answered diagnostic questionnaires in 2001-03. It was funded by the National Institute of Mental Health.

About 5 percent to 7 percent of the nationally representative sample had had the disorder, which would equal up to 16 million Americans. That is higher than better-known mental illnesses such as schizophrenia and bipolar disorder, Coccaro said.

The average number of lifetime attacks per person was 43, resulting in $1,359 in property damage per person. About 4 percent had suffered recent attacks.

The findings were released Monday in the June issue of the Archives of General Psychiatry.

The findings show the little-studied disorder is much more common than previously thought, said lead author Ronald Kessler, a health care policy professor at Harvard Medical School.

“It is news to a lot of people even who are specialists in mental health services that such a large proportion of the population has these clinically significant anger attacks,” Kessler said.

Four a couple of decades, intermittent explosive disorder, or IED, has been included in the manual psychiatrists use to diagnose mental illness, though with slightly different names and criteria. That has contributed to misunderstanding and underappreciation of the disorder, said Coccaro, a study co-author.

Coccaro said the disorder involves inadequate production or functioning of serotonin, a mood-regulating and behavior-inhibiting brain chemical. Treatment with antidepressants, including those that target serotonin receptors in the brain, is often helpful, along with behavior therapy akin to anger management, Coccaro said.

The study found that the rage disorder typically begins at age 13 in boys and 19 in girls, increases rapidly in the teen years, is less prevalent among respondents in their 40s and becomes even less so among people in their 60s.

“Is there something profoundly important about how society is changing that’s leading to this apparent increase in people not being able to control their emotions and lashing out at other people?” asked Kessler. “Is it that we’re bad parents and we’re creating these little monsters? Is television doing it?

“We know there’s an awful lot of young people who have it today and older people tell us they’ve never had it,” he said. “Whether they’re lying or not we don’t know. But, obviously, now that it’s on our radar screen we’re going to be monitoring it very carefully.”