Though it’s one of the most common psychiatric disorders in terms of lifetime prevalence, the root causes of post-traumatic stress disorder (PTSD) are still dimly understood. For a start, we still don’t know why after a traumatic event, some people develop PTSD and others don’t.
Take, for instance, the mental-health epidemic that roiled New Orleans in the wake of Hurricane Katrina. Researchers tracked 532 low-income mothers who lived in the area during Hurricane Katrina. Four years after the disaster, about 33 percent of participants had PTSD symptoms. But the majority did not.