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The Baseball Gauge Glossary

Park Factors

The park factors used on the Baseball Gauge are different than those in the Seamheads Ballparks Database. The main reason for this is that the Ballparks Database is updated yearly as new data is released from Retrosheet. The Baseball Gauge is updated daily throughout the season and requires data that is also updated daily.


There are four different park factors that are calculated:
• Runs
• Homeruns
• Homeruns (Lefthanded Batters)
• Homeruns (Righthanded Batters)

Additionaly, they include five years of data. The main season (year 3) is weighted 3 times:
• year 1
• year 2
• year 3 (x3)
• year 4
• year 5


If there has been any significant changes made to a ballpark that may affect the run envioronment, then it is considered to be a different "version" of the park and the park factor calculaton will only use data from its specific "version". For example, when the humidor was installed in Coors Field before the 2002 season, the run envioronment was altered. So when calculating the park factor for 2002, only years from 2002-2004 are included.



Denominator

The park factors are calculated on a per game basis. This means that runs/game at home are compared to runs/game on the road. A more accurate denominator of outs or at bats would be prefered and will likely be included in the future.



Adjustments

Since teams only play half of their games in their home park, it is necessary to make an adjustment that reflects the other half of their games.



Adjustment Formula

LgTms = # of teams in the league
PF = Park Factor
Adj = ((LgTms - 1) * PF + (LgTms - PF)) / (2 * (LgTms - 1))