Bank of Maimonides
And so the Great Mainstream Stat Wars of Summer 2007 continue. Ziller fires back with his critique of TOIH, and Silverbird defends our honor thus in the comments section:
A couple of points. First, it seems like you are using season-level data here (please correct me if I'm wrong about this). This presents several problems. One that has been mentioned already is that players improve, so there will be covariance between quality and minutes increased (this is something you try to account for, I recognize). Another reason is that season-to-season increases in minutes often result when players are traded/signed to weaker teams, and thus are sharing the ball with weaker teamates. Likewise, players who join better teams and play fewer minutes may see an increase in efficiency, e.g. Matt Bonner (one of the players on our list) who, when he joined the Spurs, saw his playing time fall sharply but his PER jump 20%. Both of these cases are consistent with our original argument, which is that PER inflation reflects imbalances between teams. Career level data just doesn't work here. Better would be intra-season data on large mpg increases, but here you'd have to control for things like quality of opponent (since bench players generally see more time against crappy teams). Maybe I'll try to do this at some point, when i have the time.
Second- I'm not sure why you restrict your data set only to players whose mpg increase from the previous season. What about the players whose mpg decrease? (i.e. Matt Bonner). Maybe your results will be the same. Regardless, it seems like an odd restriction. After all, the relationship you're testing for is between minutes played and efficiency, not minutes increased and efficiency.
Third- We never claim that "if you increase a player's minutes, his efficiency will suffer". I'm sorry if you interpreted it this way. What we said is that very large increases in mpg - the kind that change a bench player into a starter - will decrease efficiency, all else equal (the "else" here being age, the team played for). Again, the only way to really evaluate this claim is with within-season data.
Finally, since our entire argument was about players with above-average PERs (the group we looked at was the top 150 - that is, players who should be starters, according to Hollinger), it seems a little odd to present your overall coefficients as somehow refuting us us. Your subgroup of players with 15+ PER is really the group we're talking about. And although I certainly wouldn't claim the negative coefficient (-.22) as some vindication - it is, as you say, still very small - it certainly seems important.
This is the part where I admit that I'm beyond my depth. On a common sense level, the original Silverbird/Shoals hypothesis still makes sense to me. On the other hand, it is entirely within the teachings of FreeDarko to think that all benches are stocked with hell-bugs awaiting their moment. I would only be really bummed if NOTHING happened when these players got their added PT.
Another note: Tom and I were talking earlier today about how deadest summer is the perfect time to have this discussion. I'm aware that some people spend all season up in this vein, but here you have minds addressing these issues from a range of perspectives. Super-stats can't wholly supplant subjectivity or intuitions, and most of us involved in this debate want to talk about ways that all these facets of NBA knowledge can co-exist. These forces should feed and learn from each other; when there's a clash, it's time to figure out the interaction between the two realms, not break out the scalp knives.