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Thursday, January 26, 2012
AL v. NL in 2011
It is generally accepted in the sabermetric community that the AL is a better league than the NL, at least for the last several years. This is evidenced by the fact that the AL has a large advantage in IL games, although at least some of that edge could be something other than overall “talent”, although this is not likely and several people, including myself, have found little or no inherent advantage to the AL in IL games (e.g., the NL teams do not have any DH’s, so they have to juggle their lineup in AL parks, on the other hand, in NL parks, AL teams have to sit their DH’s or juggle their lineup, perhaps putting a bad defender - their DH - in the field, the AL pitchers typically are poorer hitters than the NL pitchers, etc.).
Since 2005 (an arbitrary beginning point mind you), the AL has a .555 WP in IL games. That is a lot! That suggests an average AL team would be a 90 win team in the NL.
My research in the past (do a search in this blog and I think I wrote a piece a while back on THT or BP) indicated that the edge has mostly been in pitching and in fact the NL may have had equal or better hitting than the AL in the last few years. Keep in mind this has nothing to do with league rpg or ERA or the fact that the AL bats 9 real hitters and the NL only 8 (plus pinch hitters for the pitcher of course). When we say that the AL is a better pitching team that means that if you took a pitcher from the AL and put him the NL, his rank among pitchers and thus his value, like WAR, would go up. Same for batters.
So one way to quantify (within some degree of certainty - actually not a whole lot) any differences is to look at players who switch leagues from one year to the next. If a batter switches from the NL to the AL and his batting lwts or WAR per x number of PA (or any other rate stat that is relative to league average) goes up then he is going to a league with less batting talent and vice versa. Again, you cannot use some non-league relative stat like OPS or ERA or FIP.
A few things about that though. One, you have to look at “switchers” from both leagues since it is possible that all players do better or worse for one year after they switch for various reasons. Two, you have to be careful about regression. Players who switch leagues are on the average below average players so their stats will naturally get better regardless of whether the new league is better or worse than the old one. Three, the results only tell us about the relative difference between one league in one year and the other league in the next year. You have to do some more gymnastics to compare leagues from the same year. For example, let’s say that in 2010 both leagues had the same talent on offense, but in 2011 the NL got better. If a hitter moves from the AL in 2010 to the NL in 2011, his league-normalized rate stats will go down even though the leagues were the same in 2010 and we don’t know yet about 2011. We only know from that example that the 2011 NL was better than the 2010 AL.
Oh, and you have to account for age of course when using this method.
Another method, and one I will present herein, is looking at IL games. For that, you have to look at lots of things, since the teams that are fielded in IL games are not necessarily the ones that are fielded in non-IL games and of course we don’t really know how to compare the pool of parks in each league (although someone can try computing PF’s based on IL game data).
Here is the basic method:
Look at how AL batters do against NL pitching in NL parks and compare that to NL batters against NL pitching in the same (NL) parks. If the AL batters do better than the NL batters in the same parks against the same pitchers, then they are the better hitting league, right? Not so fast. You have to control for the pool of pitchers and batters, especially the latter. As I said, the teams that each league fields in IL and non-IL games are not the same. AL DH’s are sometimes benched in IL games in NL Parks, and NL lineups can look completely different in AL parks. We also have to look at both sides. As with the first method, it is possible that batters in IL games do poorly just because they are facing unfamiliar pitchers or playing in unfamiliar parks. That might be true of pitchers as well.
Anyway, to compare leagues in pitching (and defense), we look at how NL pitchers do versus NL batters in NL parks and how AL pitchers do versus NL batters in NL parks. Etc. (we look at all the permutations where we control for the opposition and the park).
Lastly, we can actually look at defense somewhat independently, since UZR is not really that park or league dependent. Presumably a hard hit ground ball in the NL to location X has around the same chance of being fielded as one in the AL.
Interestingly, the AL had a huge (relatively speaking) advantage in UZR in 2011. They had a total of +47 runs and the NL had -47 runs (remember that UZR is always zeroed out each year for BOTH leagues combined and the base line for the catch rates for each bucket is always 6 years of data from both leagues). So the AL had an advantage on defense of around .04 runs per game, which is a .510 WP alone! In 2011, the AL won 52% of the IL games, so there isn’t much left, assuming that the 52% win rate is the true difference in talent between the leagues, which is unlikely (one SD by chance in 252 IL games is 3.2%, so we are 95% confident that the true difference, due to talent, is between 58% for the AL or 54% for the NL). So really, we can pretty much ignore the 52%, although the fact that in prior recent years the AL dominated, changes the Bayesian a priori estimate (going into 2011, the chances of the AL being better is large). But enough of that Bayesian nonsense!
Here is rest of the 2011 (other than above-mentioned defense - UZR):
Actually, I’ll redo the defense to look at the UZR of players actually on the field in IL and non-IL games, because we have to factor out the defense from the pitching in each bucket of games.
Let’s start with the NL batting at home versus AL pitchers (IL games). After adjusting for the pool of batters and pitchers on the field (compared to the average pool of batters and pitchers for the whole year), the NL had a lwts (it doesn’t matter what out value I use, since I am going to use the same out value for all lwts calculations) per 500 PA of -6.9 runs.
NL batting at home versus NL pitchers is -.9 lwts, or -.07 rpg. That suggests that the AL pitchers are 6 runs per 500 PA (.468 rpg) better than the NL pitchers. That is a lot. But…
Again, maybe the NL batters did worse against AL pitching only because they are not as familiar. We also have the better AL defense. Plus we are only looking at half of our sample - pitching on the road. We have to look at pitching at home.
Now let’s look at the other half of our sample.
AL batting at home versus NL visitors: 2.7 lwts runs. AL batting at home versus AL visitors: -1.9 runs. A difference of 4.6 runs. The difference in NL parks was 6 runs. We have to take the average and assume the rest is due to unfamiliarity with the pitchers or random fluctuation, or both. So the difference in pitching (plus defense) is (6+4.6)/2, or 5.3 runs per 500 or .413 rpg.
Let’s factor out defense. The AL defense in NL parks was .035 runs per 500 PA and the NL defense on the road in NL parks was -.313 runs per 500 PA, so the total difference in defense in NL parks was .348. In AL parks, the AL road defense was .408 and the NL road defense in IL games was -.781 (ouch). The difference in defense in AL parks, was 1.189. Again, we take the average of 1.189 and .348, or .768 runs per 500.
So we subtract .768 from 5.3 and we get 4.53, or .353 rpg for the AL advantage in pitching in 2011!
The batting is easier since we don’t have to worry about factoring out defense. I’ll skip the individual numbers and just give you the result.
The NL actually had a .1 runs per 500 PA advantage in batting! That is .008 rpg.
So final tally is:
Pitching
AL by .353
Batting
.008 NL
Defense
.038 AL
Total: .383 rpg AL, which is a 54.2% WP. Voila!
BTW, just based on UZR, here is how the league defense totals have swung over the years:
2004
NL +14
AL -12
2005
NL +1
Al -1
2006
NL 0
Al 0
2007
NL +8
AL -8
2008
NL -8
AL +9
2009
NL +13
AL -13
2010
NL -20
AL +18
2011
NL -47
AL +47