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September 22, 2005

Lies, Damned Lies

A New Look at Aging

by Nate Silver

This week’s column was originally supposed to be a break from the usual LDL routine, inspired by Tuesday night’s fantastic white Sox/Indians game, which I got to take in with New York Sun buddy Tim Marchman. Tim and I have some mysterious, voodoo-like power when we go to Sox games together. Earlier this year, Carl Everett, baseball’s best-known proponent of intelligent design theory, came to the plate in a game against the Twins, and Tim, who might or might not have joined me in enjoying a couple of beers, screamed “Hit One For Jesus!” Everett promptly smacked a two-run homer on the next Kyle Lohse pitch.

This time around, our powers worked in reverse: Joe Crede was up against Jake Westbrook in the bottom of the third, and we were having a lively conversation about what was wrong with Crede’s game, and how he had failed to live up to expectations. My famous last words were: “it’s making hitters like Joe Crede look stupid that keeps pitchers like Jake Westbrook in the game." Next pitch? Boom, two-run homer. Crede followed suit with his walk-off job in the tenth, a home run that bore some eerie resemblance to the Aaron Fricking Boone shot: underachieving third baseman, first pitch of the inning against a junkballing reliever, healthy shot to left field. Boone, incidentally, also hit a home run in the game, as did Casey Blake--the two Indians I had taken special care to dis in a column earlier this season. Sadly for White Sox fans, neither positive (“hey, Mitch Williams was fun!”) nor negative thoughts (“maybe Guillen really is insane”) could get Bobby Jenks to throw strikes, which would apparently take Eric Gregg’s being nominated to Sandra Day O’Conner’s vacant seat.

In any event, it was one of those games that really reinforced the notion that, as smart as we analysts might think we can be, our science can’t entirely do justice to the drama, art, and utter randomness that a September pennant race game can provide. Joe Sheehan riffed eloquently on this exact theme, which is why we’ll be moving on to a regular LDL full of graphs and charts and database searches in a moment. But I’ll conclude this detour by noting that poker theorists such as David Sklansky and Mason Malmuth have commented that poker (particularly Texas Hold ‘Em) represents a perfect balance of luck and skill: enough skill to reward correct strategy over the long run, but enough luck to allow the fish to have their days, and generally keep things interesting. Pretty much the same thing can be said about baseball.

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Today’s topic, then, is going to be on the differences in aging patterns by position. You’ll sometimes hear one of us say things like “middle infielders don’t age very well,” and while I’m sure there have been studies on this subject, we haven’t usually bothered to cite one of them. This article is intended to provide some simple benchmarks on the subject.

The method that I’ll apply is to compare the number of Equivalent Runs (EqR) produced by players at a given position and a given age over consecutive seasons. For example, if the cohort of shortstops produces an average of 70 EqR when they’re 23, but an average of 77 EqR the next year when they’ve turned 24, we can say that the average improvement by a 24-year-old shortstop is 10%. All the numbers here were pulled out of the PECOTA major-league database, which means that everything is park- and league- adjusted, and that only post-WWII players are included. Players are classified by their primary defensive position in the first of the two consecutive seasons: for example, while Alex Rodriguez became a third baseman at age 28, the study classifies him as a shortstop for that season since that’s where he played in his age-27 year.