Women are more than twice as likely as men to suffer from PTSD. Studies are underway to find out why.

In 1991, Karestan Koenen was a recent college graduate and Peace Corps volunteer who arrived in a village in Niger eager to help local women start small businesses. When her sister came to visit during Christmas, the two decided to travel north to Agadez, a city in the Sahara.
There, on the morning of Dec. 27, two male traders stopped by, trying to sell them jewelry. Koenen’s sister went to the market with one of men to have a look. While she was gone, the second man grabbed Koenen, held her down and raped her.
Traumatized by the experience, Koenen was medically evacuated to the United States two days later and resigned from the Peace Corps. She returned to New Jersey to live with her parents, but the assault continued to haunt her. Increasingly, she became depressed.
A psychologist diagnosed Koenen with post-traumatic stress disorder, or PTSD, a condition triggered by a traumatic, scary or dangerous event, and, for reasons still unclear, seems to disproportionately afflict women. These assaults can include combat, sexual assault, gun violence, accidents, natural disasters, even the death of a loved one.