Monday, February 12, 2007

Historical Park Factors

I have just posted a new spreadsheet with park factors for all teams, 1901-2004, as a Google Spreadsheet. These are five-year park factors, calculated in the same manner I describe on this page.

The guiding philosophy was to try to include as much data as possible. If there are five possible years of data to be used for a park, they will all be used, even if four of the seasons were in the past or in the future. The source of the raw data was KJOK’s excellent park database.

I treat a park as new if there are major changes to the dimensions, but I did not by any means do a complete historical survey to find out when those changes have taken place, so some that probably should have been treated differently are not. If you have specific data on when a change should have (or shouldn’t have) been made, feel free to leave a comment and I will try to incorporate these changes when I update the chart some time in the future.

Additionally, when a team moves, and a new team immediately moves in (for example, the Senators of ’60 and ’61), this is treated as a new team. Also, in cases in which teams have played a significant (which I defined as around ten or more) number of games in a different stadium in the same year, those years are treated as being a new park (an example is the Dodgers playing games in New Jersey the two years before they moved from Brooklyn). Whenever a “new park” of this sort is established, when the old order is restarted it is treated as another new park.

The reason the park factors are only shown through 2004 is that my ideal data set is two previous years, the year in question, and two future years. For most of the parks active in 2005, we will after 2007 be able to fill this dataset, and so I don’t want to publish a park factor now and change it later. However, there are a few parks where the 2004 or 2003 factors are not yet settled because they are new and there are not yet five years of data available. In these cases, I have listed a PF but marked it as one that will change in the future.

Now I will give an example of how I chose the years to be considered in figuring the PF. Suppose we look at the Diamondbacks, who have played in Bank One Ballpark since 1998. In 1998, we have no previous data, but we do have four future years of data we can use, so the sample is 1998-2002. For 1999, we have one previous year, so we take three future years, and get 1998-2002. For 2000, we have two previous years and two future years, so we use 1998-2000. In 2001, we use the two previous years (1999 and 2000), and two future years (2002 and 2003), making the total sample 1999-2003.

Let’s also consider the end of the Braves’ tenure in Fulton-County Stadium. The last season there was 1996. For 1994, we have two previous years (92 and 93) as well as two future years (95 and 96), so we use 1992-1996. For 1995, we have just one future year, so we use three previous years, and also use 1992-1996, and the same for 1996.

For a few random facts, the highest PF is for Coors Field in 1998, 124. The highest non-Coors PF is 114 for Mile High in 1993-94. The highest non-Colorado PF is 113 for the Baker Bowl in a number of years (1923-26, 1933-1937). The lowest PF is 91 for Braves Field in 1936, Dodger Stadium in 1966 and County Stadium in 1959.


  1. It would be interesting to see absolute park factors -- that is, how much easier has it become to score runs (or hit home runs, etc.) in today's universe of parks, as compared to those of one hundred years ago.

  2. ...and assuming that absolute park factors for run scoring have gone up, how much of this can be attributed to:
    -smaller ballpark dimensions
    -less foul territory
    -bigger, stronger hitters and pitchers
    -height of the pitcher's mound
    -umpires' interpretation of the strike zone
    -batters' body armor/crowding the plate and/or pitchers not brushing batters back as much as in previous eras
    -climate control/alteration of prevailing wind patterns
    -global warming
    I don't think I can accept the knee-jerk responses to increased run scoring, such as PEDs and "watered-down pitching".


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