But imagine for the moment that their numbers are OK. It could be that the intense nature of military training does what you might naively expect, and makes men more aggressive. (I don't think that would be quite as useful as training them to obey orders and how to react under fire. Just being more aggressive seems like a bad thing for discipline.) Or it could be that the military, which attracts more aggressive men in the first place, gives them life-or-death training that leaves them less interested in little white lies; and they fill out the questionnaires more accurately.
The report's author draws a different conclusion from the one you expect:
It’s striking that military service can have this long-lasting effect on people. But, on the other hand, this research also underscores that it’s really difficult to change a person’s personality. If military service is one of the most intensive experiences imaginable, and the best the military can do is a modest change on the one dimension of agreeableness, what does that say about our individual prospects for becoming, say, more outgoing, or to exercise more regularly, or to finally quit smoking?
"It kind of flies in the face," Jackson said, "of how some people wish that they had more control over changing just who they are."
How outgoing you are is personality-based, and likewise how self-controlled you are, but habits are sometimes amenable to preparation, so I'm not sure his examples are good.