Updated In-season 2010 (and 2009) Park Factors
Posted by Sean Forman on September 15, 2010
When computing park adjusted stats like ERA+, OPS+, and by extension some of the parts of WAR, in season, we have traditionally extended the previous season's park factor through to the current season. So for 2010, we've been using the 2009 park factor.
For past year park factors, we use a three-year park factors when available. So for 2008, we used an average of 2007, 2008 and 2009, and for 2009 (and by extension 2010) we used 2008 and 2009. For a new park like Target Field, we just use 100 or neutral at the start of the season.
We now have nearly 90% of the season in the books, so we have a pretty good idea of how the parks are playing this year, and since there are many decision makers and awards voters who use the advanced metrics on this site, I have decided to do weekly updates of the park factors from now until the end of the season. Every Tuesday, you should see an updated park factor on the site. This went into effect today (Wednesday), and there will be some noticeable changes to players' numbers.
Seattle has been much more of a pitcher's park than previously and New Yankee Stadium more of a hitters park than last year, meaning that the gap between CC Sabathia and Felix Hernandez may not be a gap at all and if you count unearned runs like our Pitching WAR does, Sabathia comes out ahead.
Coors Field has also returned to some of its loftier offensive levels knocking Carlos Gonzalez down even more than before, while Ubaldo Jimenez looks better than before, and is now tied for second in the NL in WAR.
Here are the changes to the Park Effects for 2009 and then 2010, in order of changes towards a hitter's park to changes towards pitcher's park. Note that the 2009 factors are now recomputed as the average of the single-year 2008, 2009, 2010 factors and the 2010 factors are the average of the 2009 and 2010 factors.
| yearID | teamID | BPF | PPF | BPF_old | PPF_old | +--------+--------+------+------+---------+---------+ | 2009 | NYA | 106 | 104 | 97 | 96 | | 2009 | TOR | 101 | 100 | 97 | 97 | | 2009 | COL | 113 | 113 | 109 | 109 | | 2009 | SDN | 90 | 91 | 87 | 88 | | 2009 | CLE | 96 | 96 | 94 | 94 | | 2009 | ATL | 99 | 98 | 98 | 98 | | 2009 | MIL | 97 | 97 | 97 | 96 | | 2009 | FLO | 102 | 102 | 102 | 101 | | 2009 | PHI | 102 | 101 | 102 | 101 | | 2009 | PIT | 97 | 99 | 97 | 98 | | 2009 | CIN | 101 | 101 | 101 | 102 | | 2009 | BAL | 100 | 102 | 100 | 101 | | 2009 | LAN | 95 | 94 | 95 | 94 | | 2009 | TEX | 104 | 104 | 104 | 104 | | 2009 | BOS | 106 | 105 | 106 | 105 | | 2009 | CHA | 104 | 104 | 104 | 104 | | 2009 | WAS | 99 | 100 | 99 | 100 | | 2009 | MIN | 99 | 98 | 99 | 98 | | 2009 | OAK | 98 | 98 | 98 | 98 | | 2009 | HOU | 98 | 99 | 99 | 100 | | 2009 | SLN | 98 | 98 | 99 | 98 | | 2009 | KCA | 97 | 99 | 98 | 99 | | 2009 | SEA | 94 | 95 | 96 | 97 | | 2009 | SFN | 102 | 102 | 104 | 104 | | 2009 | DET | 101 | 101 | 103 | 103 | | 2009 | NYN | 96 | 97 | 98 | 98 | | 2009 | CHN | 106 | 106 | 108 | 107 | | 2009 | LAA | 99 | 98 | 101 | 101 | | 2009 | TBA | 98 | 97 | 101 | 101 | | 2009 | ARI | 105 | 105 | 109 | 109 |
+--------+--------+------+------+---------+---------+ | yearID | teamID | BPF | PPF | BPF_old | PPF_old | +--------+--------+------+------+---------+---------+ | 2010 | NYA | 106 | 104 | 97 | 96 | | 2010 | COL | 116 | 116 | 109 | 109 | | 2010 | SDN | 92 | 91 | 87 | 88 | | 2010 | TOR | 101 | 101 | 97 | 97 | | 2010 | MIN | 104 | 103 | 100 | 100 | | 2010 | PIT | 99 | 101 | 97 | 98 | | 2010 | FLO | 104 | 104 | 102 | 101 | | 2010 | KCA | 99 | 101 | 98 | 99 | | 2010 | OAK | 99 | 99 | 98 | 98 | | 2010 | LAN | 95 | 94 | 95 | 94 | | 2010 | PHI | 102 | 101 | 102 | 101 | | 2010 | MIL | 97 | 98 | 97 | 96 | | 2010 | CLE | 94 | 95 | 94 | 94 | | 2010 | TEX | 104 | 103 | 104 | 104 | | 2010 | CHA | 104 | 104 | 104 | 104 | | 2010 | BOS | 106 | 105 | 106 | 105 | | 2010 | BAL | 100 | 102 | 100 | 101 | | 2010 | ATL | 98 | 97 | 98 | 98 | | 2010 | SLN | 98 | 97 | 99 | 98 | | 2010 | WAS | 98 | 99 | 99 | 100 | | 2010 | CHN | 107 | 107 | 108 | 107 | | 2010 | CIN | 100 | 100 | 101 | 102 | | 2010 | NYN | 96 | 97 | 98 | 98 | | 2010 | DET | 101 | 101 | 103 | 103 | | 2010 | SFN | 102 | 101 | 104 | 104 | | 2010 | SEA | 93 | 94 | 96 | 97 | | 2010 | HOU | 96 | 96 | 99 | 100 | | 2010 | LAA | 98 | 98 | 101 | 101 | | 2010 | TBA | 96 | 95 | 101 | 101 | | 2010 | ARI | 103 | 104 | 109 | 109 | +--------+--------+------+------+---------+---------+
I have not rerun all of the 2009 stats to reflect these changes to their park effects, but will do so soon.
September 15th, 2010 at 8:58 am
Thanks for the update. Target Field at 104/103 is certainly an eye-opener. I guess there is more to scoring than hitting home runs.
September 15th, 2010 at 8:59 am
How does CBP have such a reputation of being a band box with park factors that are awfully close to neutral? I guess the Humidor in COL has a pin hole leek and isn't doing the job as effectively. Big drop (in hitting) for minute maid park was, at least to me, the biggest surprise...
September 15th, 2010 at 9:19 am
Chase Field went from 109 to 103 ?????
Thats more than a little ridiculous. Team OPS+ went from 92 to 97 overnight.
September 15th, 2010 at 9:36 am
Technically it didn't happen overnight. It's been happening all season, we just updated the park factors to represent what was happening this season.
Keep in mind that park factors are also relative to all of the other parks in the league. Both San Diego and Colorado saw big boosts to their park factors, so that is going to make Arizona relative to them into less of a hitters' park. It's a huge change for them. Is there any evidence that they are doing something different at the park regarding the roof, a/c, etc.
September 15th, 2010 at 10:20 am
They haven't done anything different at the park, but they are actually considering all possible changes to make the park less hitter friendly, including Humidor, dimension changes, batters eye, etc. I wonder if this will affect their decision making at all.
September 15th, 2010 at 10:48 am
Is the Yankee Stadium single-season number right? Just looking at runs scored in home and away games, it looks like there are 19% more runs scored in home games, so the PF should be around 109. You have it as 115. I know there are a few other adjustments you make, but that seems like a huge difference and I wonder what I'm missing.
September 15th, 2010 at 10:52 am
Johnny, we look at home and road innings played in the park, so it is possible that there were more extra inning home games and the home team records can affect how many bottom of the ninths are available as well, so it isn't just a runs scored/allowed issue.
September 15th, 2010 at 11:08 am
I know that, but when I do off-the-cuff calculations of other parks just based on the total runs scored home and away, I don't think I've ever seen it off by more than a point or two. Seems odd that a few unplayed half-innings could cause a 6 point swing in the PF.
September 15th, 2010 at 11:10 am
Aha, I see almost all their extra-inning games have been on the road, that may explain it.
September 15th, 2010 at 11:57 am
how does cbp and att park have the same number? cbp, as mentioned earlier, has the rep of being a bandbox and att has the rep of being a big time pitcher's park.
September 15th, 2010 at 12:39 pm
Kingcrab, you will need to look at runs scored and allowed at home and road and the innings played in each to answer that question.
September 15th, 2010 at 2:11 pm
Is there any way this can get updated monthly or maybe quarterly next season?
September 15th, 2010 at 2:18 pm
I was already thinking that I would update it daily next year, perhaps something like
PF 2011 = (PF 2010 + (1-X)*PF 2009 + X* PF 2011)/2
where X = percentage of the season completed thus far.
September 15th, 2010 at 2:31 pm
If you were to run it daily, it would be important to account for new stadiums, right? For example, Target field shouldn't have 2009 numbers reflecting. I know you know that. I'm just trying to help!
September 15th, 2010 at 2:52 pm
Sean: have a hundred game or so regression to 1.00 in these. That will kill off some of the annoying motion. I made a note on Tom Tango's blog, and he's more of an expert than I in this, so he might have something to say as well.
September 15th, 2010 at 2:56 pm
This is sabermetric malpractice! How can you apply one PF to all players on a team, regardless of whether they are RH or LH, power hitters or singles hitters, speedy or slow? To show the folly of this I need go no further than Coors Field:
Home OPS - Road OPS (Career)
- Seth Smith, +.321
- Carlos Gonzales, +.289 (Rox years only)
- Clint Barmes, +.178
- Todd Helton, +.145
- Troy Tulowitski, +.121
- Colorado Rockies Team, +.220 (2010 only)
So, Coors helps everyone, but it helps some players a hell of a lot more than others. Other parks like Fenway with their idiosyncratic measurements show even more pronounced differences.
Folks here have vested interests in OPS+, WAR, etc., so I'm sure I'll get flamed, but anyone who stops to think about this for even a minute will know that I am right.
September 15th, 2010 at 3:45 pm
Kelly, your argument is hardly new enough to be worth posting in two threads.
Read Josh's response in the other thread.
There is no "right" or "wrong." What are you trying to measure? If you are measuring value, it only matters what a run is worth in a particular park. That's what B-R's park factors are trying to tell you.
September 15th, 2010 at 5:16 pm
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September 16th, 2010 at 1:54 am
I agree you need regression. Any time you are dealing with sample data, which, presumably is 100% of the time, and you are trying to find the "rrue" of something, you need to regress.
Sean, if you want, send me a file of your PF like this, and I'll tell you how many games I would add:
year,park,B_PF,P_PF
Also, what Sean does is not really PF is it? It includes opponents? So, that is a problem too if you apply it over multiple years.
What you REALLY need to do is have a factor that applies only to the park, and then a factor that applies to opponents of that year. And when you do multi-year, you do multi-year on that park-portion, and single-year on the opponent portion.