from Amazon
Saturday, October 25, 2008
Is the AL still better than the NL, and if yes, is it pitching, hitting, or both?
I wrote an article two years ago that detailed how we can determine which league is better in hitting, pitching, and overall (of course defense and baserunning should be included as well). Basically, there are two ways.
One, we can look at how players do when they switch leagues from one year to the next compared to players who don’t switch leagues.
For example, let’s say there is a league-average batter (league-normalized linear weights of 1.00) in the NL and he goes to the AL the next year. And let’s say that in the AL, his normalized lwts is 1.10, whereas the player who stays in the AL, has a league-average lwts in year I and then a league-average lwts in year II, we can assume that the batting is a lot better in the NL (and average batter in the NL becomes a better batter, relative to the league, when he goes to the AL). That assumes that both players are the same age. Obviously we can’t tell anything from one or even a few batters, but since there are usually around 30 batters who switch leagues in any given year and they get a total of over 5000 PA (using the lesser of the PA for each player), we have a decent (not great) sample size to work with.
Anyway, the other method is to look at how, for example, NL hitters do against AL pitchers in AL parks (in inter-league games of course), as compared to AL hitters in AL parks in non-inter-league games. Assuming the same pool of pitchers and batters (we can control for that), if the NL batters do better than the AL batters, then we can assume that NL batters are better. Again, sample size issues are present.
When we do these two kinds of analyses, we have to do it “both ways.” In other words, we have to check NL players who go to the AL and AL players who go to the NL and “split the difference.” The reason is this: Let’s say that NL pitchers go to the AL and get better. That suggests that NL pitchers are better. But, what if the reason they get better is that AL batters are not familiar with them. In other words, even if the league quality were equal, ANY pitcher who switches leagues would get “better.”
Well, if NL pitchers going to the AL get 10% better and AL pitchers going to the NL also get 10% better, obviously we can’t assume that one league is better than the other (they are about equal). But if an NL pitcher goes to the AL and gets 10% better and an AL pitcher goes to the NL and remains the same, then if we “split the difference,” we can assume that NL pitchers are 5% better than AL pitchers. The NL pitcher “improves” by 5% because of talent disparity between the two leagues, and then improves another 5% because he has never been seen in his new league. The AL pitcher who goes to the NL improves by 5% because he has never been seen in the NL, but gets worse by 5% because the NL is the better pitching league, for a net gain of zero.
Using the “switched leagues” method, I am going to recap the numbers from the last few years and then I’ll give you the 2008 numbers (players who switched leagues from 07 to 08).
I’ll do that for hitting and pitching. Using the numbers from this year, we can get some idea as to whether and by how much the AL still has superiority.
One other piece of data is relevant to that question this year: In inter-league games this year, the AL won 59.4% of the games, suggesting that it is the much better league. Then again, at plus or minus 2 SD, that is 53 to 65%. Last year it was 54% and the year before it was 61%. Since you would not expect any differences in the leagues to shift dramatically from one year to the next (they could I suppose), that is more evidence that the AL is better this year, as well as during the last few years.
Let’s look at some of those “league-switch” numbers.
Let’s start with batters. I am using batting lwts which are “zero’d out” for each year in each league. In order to avoid issues of batters in each league having different regression amounts from year I to year II, I “forced” the lwts for batters in both leagues in year I to be equal. For example, if the batters who moved from the AL to the NL had a lwts in year I (in the AL) of -2.0 (per 150 games) collectively and those from the NL to the AL were -5 in year I, I removed some of the really bad batters in the NL in year I in order to “force” the -5 to -2 (same as the AL to NL batters). If you don’t follow that, don’t worry about it.
Batters who switched leagues from 04 to 05:
NL to AL
N “min” PA age lwts difference between year II and year I
36 8671 31.4 -11.39 runs (they got worse)
AL to NL
34 9768 32.3 +.8 (got better)
This implies that the AL is better offensively by around 6 runs per 150 games per player. That is around .34 rpg.
We also want to look at players who do not change leagues, to see if either league got better or worse relative to itself the year before.
Players who did not switch leagues
NL 205 30.1 -2.61
AL 166 29.7 -2.60
This suggests that neither league changed much from 04 to 05, although maybe the NL got a little worse as we would actually expect these players to lose more in the NL because they are a little older (.4 years).
05 to 06
NL to AL
34 8782 30.6 -2.15 runs (they got worse)
AL to NL
24 7813 31.0 +2.36 (got better)
This implies that the AL is now 2.26 runs per player per 150 games better, which is around .13 rpg.
What about players who did not switch leagues. We are hoping that the NL got a little better relative to the AL, since the gap appears to have shrunk since the last year.
NL
230 30.3 -3.10
AL
157 29.6 -1.26
And yes, this does indeed suggest that the NL got a little better and/or the AL got a little worse, hitting-wise, as players from 05 to 06 in the NL got 3.1 runs “worse” and players in the AL, got only 1.25 runs “worse.”
06 to 07
NL to AL
30 6145 30.8 -12.43 runs (they got worse)
AL to NL
16 6116 31.1 -.12 (same)
This implies that the AL is now 6.15 runs per player per 150 games better, which is around .35 rpg, similar to 04 to 05.
What about players who did not switch leagues. We are hoping that the AL got a little better this time, relative to the NL, since the gap between the leagues appears to have gotten bigger since the last year.
NL
233 30.1 -3.43
AL
167 29.6 -2.23
No, this time the NL appears to have gotten even a little better and/or the AL got a little worse, hitting-wise.
We really don’t expect everything to match up, as we are dealing with relatively small sample sizes.
How about this year?
07 to 08
NL to AL
27 5649 29.9 +4.64 runs (they got better)
AL to NL
23 5357 32.1 -.57 (a little worse)
Wow, this implies that the NL is now the better hitting team by 2.6 runs per 150 games per player, or .15 rpg!
What about players who did not switch leagues. We are hoping that the NL got a little better, relative to the AL, since the gap between the leagues appears to have reversed.
NL
228 29.7 -1.47
AL
169 29.7 -2.10
Nope. This suggests that the AL actually got a little better, hitting-wise.
So, here is what the gap looks like, from 05-08, using this “players who switched leagues” methodology:
05
.34 AL
06
.13 AL
07 .35 AL
08
.15 NL
I’ll have to look at IL play to see how those numbers would match up to these. Next post, I’ll give you the pitching numbers.
Here are the pitching numbers. I am using normalized component ERA (NERC).
05 to 06
NL to AL
35 30.0 9196 .13 (got worse)
AL to NL
41 32.4 11142 -.22 (got better)
Implies that the AL has better pitching by .175 rp9.
No change of leagues:
NL
208 29.7 .24 (got worse)
AL
140 28.9 .34 (got worse)
Implies little change, maybe the AL got a little better from 05 to 06.
06 to 07
NL to AL
30 31.3 7864 .25 (got worse)
AL to NL
22 30.7 5731 .01 (got a hair worse)
Implies that the AL has better pitching by .12 rp9.
No change of leagues:
NL
227 29.7 .04 (got a little worse or same)
AL
166 28.3 .01 (basically same)
Implies little relative change, maybe both leagues got a little worse, since we expect pitchers to get worse by around .2 each year.
07 to 08
NL to AL
23 30.7 3113 .07 (got a hair worse)
AL to NL
31 28.2 5731 -.41 (got a lot better)
Implies that the AL has better pitching by .24 rp9.
No change of leagues:
NL
213 29.8 .31 (got worse)
AL
175 28.7 .13 (a little worse)
Implies that the NL got tougher which is the opposite of what we get for the players who switched leagues this year as compared to players who switched leagues last year.
To recap:
06
.17 AL
07
.12 AL
08
.24 AL