A study released April 17 by the Rand Corp. reported that 18.5 percent of the 1.6 million U.S. troops who have served in Iraq or Afghanistan -- or 300,000 people -- said they had symptoms of depression or PTSD because of their overseas service.

Nineteen percent -- 320,000 -- reported they had suffered head injuries, which, research shows, sharply increases these troops' likelihood of later developing PTSD. Only about half the troops had sought treatment for their mental health or head wounds, according to the report.