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2011 Park Factors Updated

Posted by Sean Forman on May 27, 2011

2011 New York Yankees Batting, Pitching, & Fielding Statistics -

Last year in August, there was a bit of a debacle when I started incorporating 2010 season stats into the park factors. Yankee Stadium III had been a much better hitters park and SafeCo a better hitter's park and adding in the 2010 season stats swung the AL pitcher WAR race (temporarily) in Sabathia's favor.

To avoid a similar problem this year and in future years I am going to begin updating the park factors around Memorial Day.

UPDATE: The Win Probability Added calculations for 2011 will also be updated daily to reflect the 2011 park factors and run scoring environment.

The Park Factors on B-R are 3-year factors when appropriate, so 2000's park factor relies equally on 1999, 2000 and 2001.

So now for 2011 since it is underway, we start with the PERCentage of the season played and

PF_2011_3yr = (PERC*PF_2011 + PF_2010 + (1-PERC)*PF_2009)/2

PF_2010_3yr = (PERC*PF_2011 + PF_2010 + PF_2009)/(2+PERC)

This should prevent violent swings in the park factors and at the end of the season we will end up with PF we were going to have throughout the offseason.

2011 pages will of course be updated daily. 2010 pages will be updated less often. To see what goes into each team's park factor you can look at the various one-year park factors listed on their team/year pages.

6 Responses to “2011 Park Factors Updated”

  1. Voomo Zanzibar Says:

    Yes. This is good stuff. Thank you.

    Um, question, though, on the main page of b-r today.
    The Boston Americans appear to be in 1st place.
    Mathematically, though, the Highlanders are ahead by .003

    Emotionally, this is unresolvable for some of us - especially first thing in the morning. Thank you for fixing it soon.

  2. Johnny Twisto Says:

    Very good point Voomo. Highlanders are clearly leading the division. Obviously there's a bug in the new park factors which has infected the standings.

  3. John Autin Says:

    Why can't I find the Pilgrims in the league table?

  4. Djibouti Says:

    Speaking of standings oddities, there's currently 5 AL teams with 24 wins but different numbers of losses

  5. BSK Says:


    At the top, you refer to Safeco as being a better hitter's park. I assume you meant pitcher's, right?

  6. 2011 Park Factors Updated » Stathead » Blog Archive Says:

    [...] 2011 Park Factors Updated: Baseball-Reference has now updated its 3-year park factors to include 2011 data. [...]