That is extremely difficult to determine. Research is just beginning. We are trying to identify the risk factors for PTSD. We have several leads, but it is difficult because such research requires a huge population pool, not all members of whom will necessarily experience trauma. We have to assess the impact of the trauma immediately and then later. Logistically, this is extremely difficult. With the Canadian Forces, we have a good pool allowing us to conduct excellent research, but such research is very expensive. Currently we are lacking funding.
We know little about what may predispose someone to PTSD. We know that the more violent, serious, intrusive, unpredictable, and opposed to the values of the victim the event is, the greater the risk that he or she will have PTSD. We know that if the victim already suffers from stress or depression, the fewer adaptive resources they will have at the time of the traumatic event, but that is difficult to test.