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Thursday, January 11
The tougher league

By Clay Davenport
Special to ESPN.com

Editor's note: The team of writers from the Baseball Prospectus (tm) will be writing twice a week for ESPN.com. You can check out more of their work at their website at baseballprospectus.com.

At the start of the season, I was expecting Ken Griffey Jr. to have a big year. That was probably my second-biggest mistake, after predicting the Astros to walk away with the NL Central title.

Sure, I knew Griffey had had three consecutive years of declining performance, and that he was leaving a power-packed Mariners lineup for a weaker Reds one. But he was also jumping from the American League to the National League.

Throughout the 1990s, the evidence of players changing leagues makes it appear that the AL has been the harder league. To demonstrate this, I'm going to use a statistic called Equivalent Average (EqA). At its roots, EqA is similar to OPS. The primary differences are that EqA includes basestealing and is adjusted for park effects and league offensive levels, making it better suited than OPS for multi-year studies. It is also expressed on a scale that is very similar to batting average; a player with a .350 EqA really is as good a hitter as the casual fan believes a guy with a .350 batting average to be.

(For more on about EqA, including an explanation of how it is calculated, you can go to the Baseball Prospectus website.)

In the study, I looked at every player who spent at least part of a year in one league and at least part of the next season in the other league. For example, in 1999-2000, the sample includes Griffey, Shawn Green, John Olerud, Vinny Castilla and Manny Alexander. Each player in the sample has his performance weighted by whichever season had the fewest outs made, with outs estimated as AB-H+CS. If Griffey made 440 outs in 1999 and 327 in 2000, his weighting is set at 327; Jim Edmonds had 157 in 1999 and 282 in 2000, so he's weighted at 157. If someone made 400 outs in 1999 and 1 in 2000, his weight would only be 1. I ignored players with a weight less than 100.

Generally speaking, you wouldn't expect individual players to hit the same in one year as they did the year before. However, when you look at groups -- the larger the group the better -- you do expect their overall performances to stay about the same. If the two leagues were equal, you'd expect to see roughly equal numbers of players improving and declining. You'd expect the overall hitting of each group to stay about the same.

But that's not what happens. Here's how players who changed leagues fared for each year from 1992 to 1999:

American League to National League

Year       EQA--Yr1   EQA--Yr2   Change
1992-'93     .261       .277       +16      
1993-'94     .260       .273       +13      
1994-'95     .248       .248         0      
1995-'96     .270       .273       + 3      
1996-'97     .259       .275       +16      
1997-'98     .262       .271       + 9      
1998-'99     .263       .287       +24      
Total        .262       .275       +13

National League to American League

Year       EQA--Yr1   EQA--Yr2   Change  
1992-'93     .264       .241       -23
1993-'94     .258       .260       + 2
1994-'95     .274       .259       -15
1995-'96     .253       .242       -11
1996-'97     .274       .262       -12
1997-'98     .266       .251       -15
1998-'99     .246       .251       + 5
Total        .263       .253       -10

In every single year, the groups of players who went from the AL to the NL had a better change in EqA than their counterparts going the other direction by at least 11 points of EqA -- and averaged a 23-point difference overall.

The players were apparently evenly matched; each had similar EqAs in Year 1 the guys going to the NL increased their EqA from .262 to .275, while the guys going to AL saw the EqA decrease from .263 to .253. The averages also speak to the likelihoods for each player; two out of three players making the AL to NL transition saw their EqAs go up, while two out of three going the other way saw theirs decline.

How about 2000? Despite Griffey's poor showing, this year is clearly following the same pattern (2000 EqAs through August 20):

American League to National League

                            
                   EqAs in                            
Player          1999     2000    Change                   
Shawn Green     .309     .297     -12   
Ken Griffey     .304     .290     -14   
Todd Zeile      .273     .291     +18   
Lee Stevens     .267     .272     + 5  
Tom Goodwin     .232     .241     + 9   
Damon Buford    .219     .259     +40   
Willie Greene   .212     .242     +30   
Joe Girardi     .214     .278     +64   
Jim Edmonds     .253     .328     +75   
Wil Cordero     .283     .267     -16   
Mike Matheny    .184     .203     +19   
Chad Kreuter    .210     .300     +90   
Totals          .261     .277     +16

National League to American League

                   EqAs in                            
Player          1999     2000    Change
Gerald Williams .271     .257     -14
John Olerud     .315     .301     -14
Mike Cameron    .283     .273     -10
Raul Mondesi    .279     .274     - 5
Carl Everett    .328     .313     -15
Brad Fullmer    .256     .289     +33
Greg Vaughn     .293     .304     +11
Vinny Castilla  .240     .185     -55
Jose Valentin   .263     .278     +15
R. Henderson    .312     .266     -46
Manny Alexander .225     .155     -70
Tony Batista    .257     .282     +25
Rich Becker     .290     .278     -12
Todd Dunwoody   .201     .191     -10
Russ Johnson    .276     .255     -21
Totals          .281     .272     - 9

A few players, like Griffey and Brad Fullmer, don't follow the majority, but the overall trend is clear.

Nine of 12 players who went to the NL have improved, five by huge margins; none of the three who have fallen did so drastically.

Of 15 players who went to the AL, 11 have declined.

You don't get ratios like that by accident; if every player had a 50-50 chance of declining or improving, then a 20 to 7 split in one league's favor would only happen three times in a thousand by chance ... yet it has happened every year since 1992.

How can you explain these results?

1. There's an age bias in the data. If more old (expected to decline) players are moving from the NL to the AL, it will hold down that transition.

Reply: That hasn't been a factor. While the players going to the AL are slightly older (29.5 years on average, vs. 29.3 going to the NL), you get the same results by restricting the set to players under 30. Or under 27. The pattern holds at all ages.

2. The DH correction factor is too weak, holding down EqAs in the AL.

Reply: The EqA formula raises the EqAs of players in a DH league by 3 percent; that's because the average player in a DH league is artificially better than players from a non-DH league. So if you're compared to average, you don't look as good.

That number was determined by looking at the difference in the EqAs of the National League, as a whole and with pitchers' batting statistics removed, over several years. The average difference between the leagues is about 3 percent; currently this season, the difference is 2.9 percent. You could make a plausible argument that, since the pitchers are replaced by better-than-average hitters, the adjusted factor should be slightly higher. To get the switching players to even out, though, the adjustment would have to be on the order of 8 percent. That's something like 60-70 points of OPS, or 20 points of EqA, and the only way you're going to get that is if the average DH hits like Edgar Martinez. The answer isn't there.

3. The AL is a tougher league than the NL. If the average AL hitter were better than his NL counterpart, you'd expect this kind of result, because EqA compares the player's performance to the league average. If the average hitter got worse, and the player himself did not change, his performance relative to average would go up. And that is what I think we're seeing.

Clay Davenport writes for the Baseball Prospectus, the annual book by the same name, covering over 1500 players with in-depth statistical analysis and hard-hitting commentary. Clay may be reached at cdavenport@baseballprospectus.com.


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