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Park factor is an estimate of a ballpark’s effects on batting and pitching and is expressed as either a decimal or a whole number. A neutral ballpark has a park factor of 1.00 or 100. Park factors are those used in Total Baseball, and include threeyear averages unless a ballpark was in use for less than three seasons. Park factors are also adjusted to reflect the fact that a batter or pitcher does not face his own team. Thus, different park factors are provided for a team’s batters and pitchers. For more information, see Total Baseball’s essay on park factors. The method for figuring park factors is available in the Total Baseball glossary. A table of batters’ park factors (BPF) and pitchers’ park factors (PPF) for every team since 1876 is available here.
Adjusted ERA (AERA) is earnedrun average adjusted for league ERA and pitchers’ park factor. The formula is as follows: LgERA/ERA*PPF Here is the calculation of Pedro Martinez’s 1999 season. Martinez had a 2.07 ERA, while the American League ERA was 4.86. The Red Sox’s pitchers’ park factor was 1.02: 4.86/2.07*1.02=2.40 The decimal is dropped so that 2.40 becomes 240. A leagueaverage performance is 100.
Pitching runs (PR), developed by Total Baseball’s Pete Palmer, is an estimate of the number of earned runs prevented beyond the league average adjusted for pitchers’ park factor. The formula is as follows: [(LgERA*PPF)ERA]*IP/9 Here is the calculation for Pedro Martinez’s 1999 season. Martinez pitched 213.3 innings and had a 2.07 ERA, while the American League ERA was 4.86. The Red Sox's pitchers’ park factor was 1.02: [(4.86*1.02)2.07]*213.3/9=68 Thus, Martinez prevented an estimated 68 runs beyond the league average. A leagueaverage performance is zero. For more information, see Total Baseball’s essay on pitching runs.
Adjusted OPS (AOPS), called adjusted production in Total Baseball, is onbase percentage plus slugging average adjusted for league OBP and slugging average and batters’ park factor. The formula is as follows: [(OBP/LgOBP)+(Slg/LgSlg)1]/BPF Only nonpitchers’ OBP and slugging average are used to calculate adjusted OPS. This eliminates the comparative advantage NationalLeaguers would have over AmericanLeaguers since pitchers do not bat in the American League. A table of nonpitchers’ OBPs and slugging averages for every season since 1876 is available here. Here is the calculation of Mark McGwire’s 1998 season. McGwire had a .470 OBP and .752 slugging average, while the National League OBP was .339 and slugging average was .358 excluding pitchers. The Cardinals’ batters’ park factor was .99: [(.470/.339)+(.752/.358)1)]/.99=2.51 The decimal is dropped so that 2.51 becomes 251. A leagueaverage performance is 100.
Batting runs (BR), developed by Total Baseball’s Pete Palmer, is an estimate of the number of runs contributed beyond the league average adjusted for batters’ park factor. The formula is as follows: (.16*H)+(.31*(TB+BB+HBP))+(.3*SB)(.6*CS)(BPF*LOV*(ABH)) The values are the result of Palmer’s 1978 computer simulation of every majorleague game since 1901. The league out value (LOV) fluctuates with league offensive levels. An out is costlier in highscoring seasons than in lowscoring seasons. Only nonpitchers’ statistics are used to calculate league out value. This eliminates the comparative advantage NationalLeaguers would have over AmericanLeaguers since pitchers do not bat in the American League. The league out value is calculated using this equation: [(.16*H)+(.31*(TB+BB+HBP))]/(ABH) Although a more precise number may be used, a league out value of .3 works well for most recent seasons. A table of league out values and nonpitchers’ statistics for every season since 1876 is available here. Here is the calculation of Mark McGwire’s 1998 season. McGwire had 152 hits, 383 total bases, 162 walks, six hit by pitch, one stolen base, and zero caught stealing in 509 atbats. The Cardinals’ batters’ park factor was .99. The league out value was .286: (.16*152)+(.31*(383+162+6))+(.3*1)(.6*0)(.99*.286*(509152))=94 Thus, McGwire contributed an estimated 94 runs beyond the league average. A leagueaverage performance is zero. For more information, see Total Baseball’s essays on linear weights, batting runs and stolenbase runs. 