Printer-friendly

June 29, 2008

Lies, Damned Lies

Home-Field Advantages

by Nate Silver

Home-field advantage is making a little bit of a comeback this year, with the home team thus far having won 56.2 percent of major league baseball games. This is actually down a few ticks from where it was several weeks ago; at the beginning of June, home teams had won almost 58 percent of their games. Nevertheless, this is quite high by the standards of recent history. Prior to World War II (when travel was more burdensome and road trips much longer), home-field advantage was more profound in baseball, but since then it has been exceptionally stable, with the home team winning about 54 percent of games each season. So, is there something systematic that is causing the home-field numbers to increase this year? Or has it just been some kind of statistical fluke?

To address this question, we first need to consider why home-field advantage exists in the first place. In baseball, the home team has a couple of built-in tactical advantages: in the National League, for example, by batting last it can pinch-hit for the pitcher while getting one extra inning out of him. Regardless of league, the home team knows exactly how many runs it needs to play for, which making ninth-inning strategy easier.

However, there are other elements that differ from park to park. Some parks favor hitters, and some favor pitchers. Some parks are asymmetrical—favoring batters that hit from a certain side of the plate—whereas others treat all hitters equally. If teams are becoming more aware of such differences and more aware of how to exploit them, that could explain the uptick in home winning percentage.

Let’s examine six or seven variables that might conceivably be related to home-field advantage, rating each major league ballpark from 1 (lowest) to 5 (highest) based on a somewhat subjective assessment of those categories.

Asymmetry