Park Factors can be calculated in a myriad of ways. The following are general park factors - which measure the overall impact of the parks a team plays in on run scoring.
I start by taking two ratios: 1) runs scored per batter inning at home versus road and 2) runs allowed per inning pitched at home versus road. I then compare these two ratios to the MLB-wide average. It turns out that major league teams have scored more runs at home than on the road per batter inning by 5.2% in 2003, even though road teams have scored more runs than home teams (5781 versus 5748). This, of course, is because home teams often do not bat in the 9th inning. Conversely, on the road, (visiting) teams score only 95.1% as efficiently as their opponents.
The average of these two ratios for each team (compared to the MLB norm) is the starting point for my park factors. Each team's park factor is adjusted for the road parks that team plays in. The factors that result are meant to apply to a particular team's batting or pitching stats; that is, they account for the fact that they play roughly half their games on the road. Because pitchers and hitters do not have the same inning distribution (pitchers get a larger share of their innings at home than batters), there are separate park factors for each group. The numbers are adjusted so that the average for each league is 1.00. These factors are not adjusted, however, for the quality of opposition faced by the hitters or pitchers of a particular team.
American League
National League
A few surprises here, to be sure. Dodgers Stadium, historically one of the best pitcher's parks in baseball has been neutralish (actually, the PF slightly favours hitters). Keep in mind that this is only 40 or so games at home and road, so there is bound to be lots of randomness in the data. Weather can affect season to season PF data, as well as whether particular starting pitchers pitch more at home than the road.
If you use 60% last year's and 40% this year's PFs, you ought to get a good read on the value of a particular player's batting or pitching stats.
I start by taking two ratios: 1) runs scored per batter inning at home versus road and 2) runs allowed per inning pitched at home versus road. I then compare these two ratios to the MLB-wide average. It turns out that major league teams have scored more runs at home than on the road per batter inning by 5.2% in 2003, even though road teams have scored more runs than home teams (5781 versus 5748). This, of course, is because home teams often do not bat in the 9th inning. Conversely, on the road, (visiting) teams score only 95.1% as efficiently as their opponents.
The average of these two ratios for each team (compared to the MLB norm) is the starting point for my park factors. Each team's park factor is adjusted for the road parks that team plays in. The factors that result are meant to apply to a particular team's batting or pitching stats; that is, they account for the fact that they play roughly half their games on the road. Because pitchers and hitters do not have the same inning distribution (pitchers get a larger share of their innings at home than batters), there are separate park factors for each group. The numbers are adjusted so that the average for each league is 1.00. These factors are not adjusted, however, for the quality of opposition faced by the hitters or pitchers of a particular team.
American League
Team --------- Batter Pitcher (2002)
Toronto ------- 1.130 1.136 (0.988, 0.988)
Kansas City --- 1.110 1.118 (1.117, 1.126)
Texas --------- 1.074 1.081 (1.099, 1.106)
Boston -------- 1.054 1.055 (0.961, 0.960)
Minnesota ----- 1.035 1.036 (0.978, 0.976)
White Sox ----- 1.028 1.029 (1.038, 1.040)
Tampa Bay ----- 1.023 1.027 (0.984, 0.983)
Anaheim ------- 0.976 0.975 (0.968, 0.965)
Detroit ------- 0.959 0.957 (0.946, 0.941)
Oakland ------- 0.949 0.947 (1.033, 1.035)
NY Yankees ---- 0.936 0.932 (0.965, 0.963)
Cleveland ----- 0.913 0.908 (1.024, 1.023)
Baltimore ----- 0.909 0.901 (0.958, 0.957)
Seattle ------- 0.903 0.899 (0.943, 0.939)
National League
Team --------- Batter Pitcher (2002)
Arizona ------- 1.146 1.153 (1.065, 1.069)
Colorado ------ 1.119 1.130 (1.183, 1.200)
Montreal ------ 1.099 1.108 (0.984, 0.985)
Houston ------- 1.032 1.034 (1.060, 1.062)
Cincinnati ---- 1.016 1.015 (1.079, 1.083)
Los Angeles --- 1.012 1.013 (0.937, 0.932)
Cubs ---------- 1.001 1.002 (0.989, 0.988)
Atlanta ------- 1.000 1.000 (0.999, 1.000)
San Francisco - 0.984 0.982 (0.939, 0.933)
Milwaukee ----- 0.971 0.972 (0.981, 0.978)
Philadelphia -- 0.968 0.967 (0.906, 0.901)
San Diego ----- 0.963 0.958 (0.956, 0.951)
St. Louis ----- 0.959 0.955 (0.975, 0.972)
NY Mets ------- 0.923 0.921 (0.922, 0.918)
Pittsburgh ---- 0.919 0.912 (1.053, 1.055)
Florida ------- 0.887 0.878 (0.974, 0.972)
A few surprises here, to be sure. Dodgers Stadium, historically one of the best pitcher's parks in baseball has been neutralish (actually, the PF slightly favours hitters). Keep in mind that this is only 40 or so games at home and road, so there is bound to be lots of randomness in the data. Weather can affect season to season PF data, as well as whether particular starting pitchers pitch more at home than the road.
If you use 60% last year's and 40% this year's PFs, you ought to get a good read on the value of a particular player's batting or pitching stats.
