Well, there are two parts to this thing.
It is very difficult to screen and predict who is going to get PTSD. They attempted to do that in World War II, and basically you could flip a coin and be as effective as our screening procedures. So it's difficult to predict. Even if you say this person is vulnerable to developing PTSD, it does not mean that he or she necessarily will, and they may actually perform quite well in theatre. So the issue of screening is difficult.
The other thing is that we don't have a whole lot of stupid people in the military. They are actually very bright and well educated nowadays, and if they decide they want to go, for the most part they know how to answer the questionnaires.
The question was asked earlier, but what I found in my research is that 50% of the people I identified as having PTSD rated their emotional and psychological health as good or excellent, which tells me that they really didn't have a whole lot of insight. The problem, they said, was I'm fine, but you guys are all messed up.
So in an ideal world, it would be great if we could actually screen and pick these people out and therefore be proactive and protect them. But I'm not aware of anything that we have at our disposal at this point in time that can actually do that. If a person has severe PTSD and you're observing them, yes, you could probably pick them out. But you have 800 people in a battalion, and you just don't have the time to be doing that, so you'd be doing it by questionnaires, and questionnaires are fallible.