[Peter_Spaeth]

Originally Posted by nat

There are lots of ways the counterfactual situation of picking a young player to start a team could be spelled out. You could go just from scouting reports of the guys when they were 20 (this is the first possibility that I mentioned).

But the assumption that I made for the exercise was that we know how their careers actually turned out. Since it's all counterfactual anyway, we can give ourselves that knowledge if we want. And why not? We do, in fact, know how they turned out. Now, given that their careers turned out one way, it doesn't guarantee that they will turn out that way again - which is why this question isn't just "which player in fact had the greatest career". But it does give us some indication of how we should expect them to turn out if they played their careers again, and what my post was doing was trying to figure out what we should expect from them if they went back in time and played their career out again.

Think about it this way: imagine that we have exact replicas of Mays, Mantle, Trout, etc. as young men. Up until the age of 20 (or whatever) both nature and nurture have, for these clones, been exactly the same as they were for the real Mays, Mantle, etc. We don't know what they're going to do with their respective careers. But we do know what their exact duplicates did with their careers, and that should tell us something about what to expect from the young ball players that we have to choose between.

It's beyond me why, if we know how they turned out, we would even ask how would they turn out if they started again. As I said, this seems an odd mix of ex ante and ex post, why not just do one or the other?