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Tuesday, January 30, 2007
Home Field Advantage
Phil points to the latest BEPRESS issue, where Phil says:
They start by examining run scoring: they find that in games of 2004-2005, the home team scored .093 runs per game more than the visiting team. This number looks small, and so the authors conclude this “little supports” the explanation that home teams are “more proficient at scoring runs.”
Ah, the power of picking and choosing numbers, without context. Here’s the reality:
Home teams allowed 11650 runs in 2004, and scored 11726 runs.
That difference is a miniscule 76 runs in 2428 games (or 0.03 runs). In effect, you are just as likely to score at home than on the road! Not.
Home team batters hit in 21092 innings, while their pitchers pitched in 22302 innings. On a per 9 inning basis, we get the following:
runs scored: 5.00
runs allowed: 4.70
That difference is a whopping 0.30 runs!
Here’s the base data:
http://www.retrosheet.org/boxesetc/YS_2004.htm
In 2004, the home teams actually won .535 times, slightly more than the above estimate.
How about 2005? The home team winning percentage was .537. The RS and RA were 11345, 10980 (difference of 0.15 runs). On a per 9IP basis, the numbers are: 4.86 RS, 4.44 RA for a difference of 0.42 runs. So, the home team winning percentage was a bit less than estimated.
Put it together, and the home team winning percentage is 0.536, with a run differential of 0.36 runs.
PythagenPat would estimate this winning percentage (4.93 RS, 4.57 RA) as ..... 0.536.