Friday, July 6, 2007

Alternative Statistics

"We keep a log on outfielders who charge the ball and who don't charge, who have accurate arms and powerful arms. We take all that into consideration. This is not a blind experiment to say hey, run until you get thrown out." - Los Angeles Angels' manager Mike Scioscia

Baserunning is often overrated. In particular, you hear broadcasters go nuts talking about the virtues of being aggressive. Most of the time, mindless aggressiveness leads to outs. In fact, it is the Angels themselves who seemed to popularize this style of play. When the won the World Series in 2002, people went bonkers over their "productive outs" approach, ignoring the fact that they pounded the snot out of the baseball in October.

I don't like the Angels. I don't like "productive outs." I don't like "small ball." Most of you probably already know this. However, this shouldn't blind one to otherwise sound research. If the Angels have a plan, and it's objectively sound, and they execute it, more power to them. The type of aggressiveness presented above isn't a bad idea at all. In fact, it's a great idea. That is the way that teams should be coaching their players. It's way better than the mindless aggression espoused by many commentators.

Someone who seeks to understand baseball can never dismiss out of hand research (as opposed to commentary) that runs counter to his or her predisposition or biases. The goal is always to incorporate new research with the old to constantly perfect the art and science of baseball strategy.


die Amerikanerin said...

This hasn't much to do with your post, it's just a request. Can you explain something about PECOTA and possibly how it works? Bob mentioned it, and I'm curious.

John Lynch said...

Sure thing.

PECOTA is Baseball Prospectus' player projection system. Essentially, it's a series of algorithms that predict player performance for upcoming seasons. Its name is an acronym, but what it stands for isn't important.

PECOTA operates by trying to find players who are historically comparable to the player it is projecting. It uses not only baseball statistics, but also physical attributes and position information to make the projections. It produces a series of projections for each player for five years into the future, each projection weighted by its probability of occurring, thus accounting for the inevitable error in the system.

Whether or not the process of using comparables to project future performance is the "right" way to project player performance is a matter of some debate. It does make some intuitive sense, but there has never been a real scientific evaluation of the methodology (or at least, not one that Baseball Prospectus has made publicly available). It would be nice to see BPro break down the results of PECOTA beyond a simple overall accuracy score.

The bottom line is that PECOTA is probably the best publicly available projection system. Keep in mind that this means that it is still wrong a lot (if only baseball were so easy), but not as wrong as other systems, like wishcasting, pulling names our of a hat, or simply expecting a guy to play as well as he did last year. Furthermore, only PECOTA is going to give you an estimate of how likely it is to be wrong (though again, this is the number that really needs to be validated).