I was having an argument with a friend the other day. It went vaguely like this,
Friend: "I'm not very disciplined. At some point I'm going to buckle down and train myself to be much more disciplined."
Me: "From experience and from what I know about humans, that's not going to work."
Friend: "Why? Motivation can come from within. If you can just train yourself like you're in the army, then you can become just as self disciplined as a soldier."
Me: "Yes, but the reason why people in the military are disciplined is because they have social incentives to be. In order to become disciplined, you need to create an environment for yourself that shapes your motivation. You can't just wake up one day and become a soldier."
Friend: "Sure, you might have to set up some environment like that. But once you've trained yourself, the discipline will stick, and you will be able to self motivate yourself from then on."
Me: "This theory would predict that people who were trained in the military would be much more productive three years after their service, compared to people who were never trained in the military. Do you agree?"
Friend: "Yes, I think that is likely."
Me: "I disagree. They might be slightly more productive but I'd predict it would be pretty similar."
So who is right?
I haven't been able to find direct research, but this seems like a classic instance where a debate can be settled by simply referencing a high quality experiment.
Data from periods of forced conscription would correct for that bias, but would introduce the new bias of a 4-F control group. Is there a fancy statistical trick to combine the data and eliminate both biases?
Draft lotteries provide randomized experiments. The most famous one is the Vietnam draft analysis by Angrist 1990 where he finds a 15% penalty to lifetime income caused by being drafted. There's also little evidence of any benefit in Low-Aptitude Men In The Military: Who Profits, Who Pays?, Laurence & Ramberger 1991, which covers Project 100,000 among others, which drafted individuals who would not otherwise have been drafted either as a matter of policy or, in the ASVAB Misnorming, unrealized accident. (As Fredrik deBoer likes to say, if there's any way it can possibly be a selection effect, then yeah, it's a selection effect.)