We published a paper in 2007 using the Canadian Forces data set, the same data set, basically showing what Senator Dallaire really talked about in his book, that Canadian soldiers who had been involved in combat or witnessed atrocities like human massacres were at about two to three times the risk of developing not just post-traumatic stress disorder but also major depression, alcohol problems, a self-perceived need for mental health.
Really, that's very consistent with the other studies in the U.S. and the U.K. The important message, still, is that most soldiers are resilient and do not develop any mental health problems, but a small number, probably about 20% to 30% who have been exposed to a high level of combat or a high level of witnessing atrocities like Rwanda, will develop a range of mental health problems--most commonly, depression, post-traumatic stress disorder, alcohol abuse, and panic disorder.