Psychiatrists and psychologists who have worked with the military say the sought-after mental profile is based largely on two well-known kinds of testing. One is a 44-item questionnaire that assesses personality. The other test is intended to gauge performance.

People who excel in combat tend to be assertive, active, excitement-seeking and enthusiastic.

“I hate to use the cliché, but these are guys who love to be at the tip of the spear,” said a psychologist who works with the military; he asked that his name be omitted to protect that relationship. “It’s more than the camaraderie; there’s a need to protect life, directly — and if necessary, to take life.”

The performance measure has more to do with attention and decision making. It is based in part on a theory of concentration “styles,” developed by researchers studying athletes.

“The classic analyst takes in the information and then retreats into their head and wants to think about it, then maybe checks the environment again and thinks some more,” said Dr. Charles A. Morgan III, a psychiatrist at the University of New Haven who has worked extensively with Special Operations forces. The elite combat troops operate much differently, he said. “They immediately take in their surroundings; they have a high degree of external focus. But they’re able to switch internally, make a quick decision — then act and adjust as they go.”

In training and in combat, this intense awareness and decision making become much sharper. “Essentially the decision making and acting become second nature,” said Bret Moore, the deputy director of the Army’s Warrior Resiliency Program of the Regional Health Command-Central in San Antonio. “You do not want these guys thinking too much.”

That may help explain the recent suicide findings. The research team, led by Dr. Kessler of Harvard and Dr. Robert Ursano of the Uniformed Services University of the Health Sciences, analyzed 496 suicides among men in the Army from 2004 to 2009. The risks for two jobs — infantryman and combat engineer — were higher across the board, at 37 per 100,000 each year. But the rate was 30 per 100,000 while deployed, compared with 40 per 100,000 when back home. The rate across the rest of the Army was much lower at home, 15 per 100,000, compared with during deployment, where it was 22 per 100,000.