There are many reasons. Traditionally, in most militaries and most of our allies, it's the junior members of the army, specifically the combat arms. We did see an uptick in that group, which has sort of settled down in the last few months. You can't absolutely say, but it also does reflect the people who are exposed most likely to the war, and they're in the trenches more often.
When we have 2,700 people or so deployed to Afghanistan, the few hundred people who are part of the battle group that spend most of the time outside the wire are certainly impacted.
There are also other theories. Junior members of the air force tend to be more technical, and tend to have different types of duties, and maybe different personalities are attracted. Certainly, if we're going to look at the near past for most of our military and our allied militaries, the conflicts in Afghanistan, Iraq and such can probably explain some of the differences. However, association and causality are, of course, two different things.