Monday, January 26, 2009

Historical Park Factors, 1901-2006

I have just posted a new spreadsheet with park factors for all teams, 1901-2006, 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 for past seasons and various sources for the 2008 data.

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 2006 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 2007, we will after 2009 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 2006 or 2005 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 (this is indicated with an orange shading; park factors for the first year after a switch are in pink text).

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 there is four future years of data, so the sample is 1998-2002. For 1999, there is one previous year, so we also look at three future years, and get 1998-2002. For 2000, there are two previous years, so we use two future years, and have a sample of 1998-2002. This is now in the ideal format of the year in question, plus the two immediately prior and future years. Of course, in 2001, we use the two previous years (1999 and 2000), and two future years (2002 and 2003), making the total sample 1999-2003, and it will continue in that manner until something changes.

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.

Terpsfan101 has also published historical park factors recently, and here is a link. His differ from mine primarily in that they use more than five years of data when applicable (with a corresponding decrease in the amount of regression used). He includes both R/O and R/PA park factors (mine are based on R/G, which is strongly correlated to R/O), has home run factors, and also includes the nineteenth century.

Historical Park Factors, 1901-2006

10 comments:

  1. I actually abadoned the idea of a R/PA park factor after the e-mail exchange we had a month ago. You had stated that you would need to use an R/O park factor if you wanted to move a player to another ballpark. I think that I misinterpreted this. Did you mean that it would still be OK to use an R/PA park factor if you were just park-adjusting a player's stats for the ballpark he actually played-in?

    For the record, an R+/PA park factor was mathematically identical to an R/O park factor.

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  2. I'm not sure what I meant either. Welcome to the club.

    My main point is that a R/PA park factor doesn't account for the fact that the player's batting line includes extra (or fewer) PA that he got as a result of the park. An out-based PF sidesteps this problem because there are 27 outs/game whether you play in Petco or Coors.

    The out-based just consolidates two steps into one. If you apply the R/PA factor, and then apply a PA factor (which no one actually figures, but one could), you can account for both effects.

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  3. Why a new park factor for Minnesota in 1994? Neither the dimensions or the playing-surface were altered that year.

    Cleveland should have a new park factor in 1933, 1934, and 1937. In 1932 the Indians played 47 games at League Park, and 32 games at Cleveland Stadium. In 1933 they played the entire season at Cleveland Stadium. From 1934 to 1936 they played all but 1 home-game at League Park. From 1937-1946 they split time between the 2 stadiums.

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  4. You also have a new park factor for Houston in 1994. There are no documented park-changes that year for the Astrodome.

    In 1997, Tiger Stadium wasn't altered.

    In 1996, Oakland only played 6 games in Las Vegas. You said that 10 home-games played in another stadium during the same season was one of the criteria for a new park factor.

    You also don't need to use a new park factor for the Mariners in 1995. When the ceiling tiles collapsed in the Kingdome in 1994, the Mariners were forced to play the last few weeks of the strike-shortened season on the road. All of those games counted as road games.

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  5. Oakland should have a new park factor in 1996. I mistakengly told you that they didn't need a new park factor that year.

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  6. It has been some time since I actually compiled the list of park changes--I'll have to see if I can dig up my notes to see why I changed those at the time. Doing some checking with Green Cathedrals, you are right about CLE, DET, MIN, & SEA.

    According to that book, though, the Astrodome foul lines were brought in five ft in '94 (although they had been moved back 5 ft the previous yr, so I didn't handle this consistently apparently), and the power alleys were moved in 5 ft (back to 1992 distance) and the fence was dropped 2 ft between the foul pole and scoreboards. I'm not sure that is enough to justify a new PF, but there were at least minor changes.

    Thanks for the review. I'll make some changes when I get a chance.

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  7. I've decided to re-do my PF's. I will now use no more than 5 years of data and I will use fewer park versions.

    You are right about the Astrodome. I was using KJOK's park data. The changes you mentioned are listed on Munsey and Suppes website.

    Can you see what your Green Cathedrals book says about the dimensions of Sportsman's Park. I am getting conficting reports about when they changed their dimensions in the 1920's. What does Green Cathedrals list as the original dimensions in 1909 and what changes until 1931?

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  8. According to Green Cathedrals, the dimensions were changed within the first month of the park being open. That made it 350 in LF, 414 in LC, 430 in CF, 270 in RF.

    Changes were:

    LF--340 in 1921, 356 in 1922, 355 in 1926, 360 in 1930, 351 in 1921
    LC--404 in 1911
    CF--420 in 1926, 450 in 1930, 445 in 1931
    RF--315 in 1921, 320 in 1925, 310 in 1926

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  9. According to Green Cathedrals, the dimensions were changed within the first month of the park being open. That made it 350 in LF, 414 in LC, 430 in CF, 270 in RF.

    Changes were:

    LF--340 in 1921, 356 in 1922, 355 in 1926, 360 in 1930, 351 in 1921
    LC--404 in 1911
    CF--420 in 1926, 450 in 1930, 445 in 1931
    RF--315 in 1921, 320 in 1925, 310 in 1926

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  10. Thanks Patriot. I might have to buy a copy of Green Cathedrals.

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