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Tuesday, July 1
NL finally grabs upper hand over AL

By Clay Davenport and Nate Silver
Special to

This Time It Counts. No more 11-inning ties, no more epic Robert Fick-Mike Williams duels with the game on the line, no more John Kruk bailing out against Randy Johnson. We're talking Pete Rose pulling a Larry Csonka on Ray Fosse, Kevin Brown throwing 60 pitches on short rest, Pedro Martinez brushing Barry Bonds off the plate. Home-field advantage is on the line, and in the days of ThunderStix, Rally Monkeys, and seven-game World Series ...

Stop us if you've heard this one before. The All-Star Game will mean something this year -- a little bit too much if you want our opinion -- but there were 250 games just completed that really counted, the longstanding early summer tradition known as interleague play. Although the American League held its own over the past weekend, sweeping cross-town series in New York and Los Angeles, the National League came out ahead on the season, winning 54 percent of the contests.

Rondell White

While the strong attendance recorded in the interleague games is a feather in the cap of commissioner Bud Selig, we suspect that the whole experience is one that AL senior adviser Gene Budig could have done just as well without. After seeing his league draw the short interleague straw, Budig may now be considering pulling a Monty Burns and bringing in a squad of ringers to improve his side's chances in the All-Star Game (Hey Mattingly, I thought I told you to shave those sideburns!). The AL's weak underbelly seems to have cost it in interleague play, and it could cost it again come All-Star Tuesday.

Before we jump to conclusions, however, a fuller examination of the data is in order. Baseball is a funny, random sport; a set of 250 games might seem like a lot, but it may not be enough to provide categorical proof of a league's superiority.

Imagine that all the interleague games were played between teams of equal strength; from a mathematical point of view, this is the equivalent of flipping a coin 250 times. The odds that the coin would come up heads at least 136 times -- which corresponds to the 136 interleague games that the NL won -- is 9.2 percent. Certainly, the National League's success is a point in its favor, but it's hardly an open-and-shut case.

In reality, the NL's argument is somewhat weaker than that. One of the lovely quirks of combining interleague play with leagues of unequal numbers of teams is that it cannot be accomplished with a balanced schedule. While every AL team was scheduled to play 18 interleague games, NL teams could play 12, 15, or 18 contests, depending on their division and the whim of schedule guru Katy Feeney. As luck would have it, the three NL teams with only 12 games apiece were all below average squads -- the Reds, Pirates, and Brewers. By having three of its weaker teams pulled out of the pack, the NL had the deck stacked in its favor, increasing its expected winning percentage in interleague games to .506.

In fact, however, we need not restrict ourselves to the 250 interleague contests in order to draw lessons about league strength. We're living, after all, in an era of high roster volatility, and there are a great number of players who have played in both the NL and the AL at some point in the recent past.

There are, for example, seven position players who started regularly for AL clubs in 2002 who have since become regulars in the 2003 National League. Using Equivalent Average ("EqA"), an overall measure of offensive production that adjusts for the run-scoring environment of a player's park and league, we can evaluate how those players have performed after switching circuits.

AL, NL Crossovers 2002 EqA (AL) 2003 EqA (NL) Change
Jim Thome .369 .305 -.064
Ivan Rodriguez .298 .296 -.002
Ray Durham .296 .311 +.015
Jose Cruz .267 .290 +.023
Rondell White .236 .285 +.049
Robert Fick .274 .293 +.019
Randall Simon .276 .251 -.025
Average .288 .290 +.002

Some observers have cited Jim Thome's performance -- he's been good, but not quite as good as we've come to expect of him -- as evidence that the NL is currently the stronger league. But while Thome's performance has been disappointing, other NL newcomers have done just fine. AL émigrés Jose Cruz and Ray Durham are having breakout seasons in San Francisco; Rondell White, forgotten about in the Yankee outfield, could be San Diego's All-Star representative; even good ol' Robert Fick is having a nice season. Taken as a whole, this group of crossover players has performed neither any better nor any worse since moving to the NL.

Comparing performances in this fashion is a nice idea, certainly, but as we'd be the first to point out, seven data points is hardly enough to draw any sort of conclusion. We could expand the list some by including players like Erubiel Durazo who have moved in the other direction, but even so, that's scant evidence to work with. A more creative approach is in order.

One such idea is to use a third league as a standard reference point. Baseball Prospectus has been employing this approach for years in order to translate minor-league statistics into their big-league equivalents, but it can just as easily be used to run a comparison of the two major leagues. Roberto Alomar and Omar Vizquel, for example, both appeared in the AL in 2001. Vizquel has remained in the Junior Circuit, while Alomar has migrated to the NL. By comparing their performance -- in this case, Vizquel's numbers have held up a little bit better than Alomar's -- we can learn a little something about the relative strength of the two leagues. One data point won't tell us a whole lot, but pull enough together and we've got a sizeable sample on our hands.

Let's take the 2001 NL as a reference point. First, we'll look at all players who appeared in both the 2001 NL and the 2003 AL. We'll weight their performance by the lesser number of plate appearances that they accumulated between the two leagues, something we'll call Common Plate Appearances or CPAs (for example, a player that had 575 plate appearances in the 2001 NL, and 265 plate appearances in the 2003 AL comes out with 265 CPAs, the smaller of the two figures). All told, there were 6,265 CPAs between the 2001 NL and the 2003 AL. Measuring by Equivalent Runs (a close relative of EqA), the group of players produced runs at a rate 1.040 times higher in the 2003 AL than in the 2001 NL, suggesting that the 2003 AL was a somewhat easier league -- the same set of players are more productive in it.

By comparison, there were 32,470 CPAs between the 2001 NL and the 2003 NL -- the numbers are much higher because, free agency and all, most players stay within their league. This time around, our group of players was less productive in the 2003 NL, producing .965 times as many runs as they had two years ago.

So, players who played in both the 2001 NL and the 2003 AL did better in the 2003 AL, while players who played in both the 2001 NL and the 2003 NL did worse in the 2003 NL. That might tell us something. By evaluating the two figures -- that is, taking a ratio of the ratios, we can quantify the difference between the two leagues circa 2003. In this case, a ratio of (.965/1.040) suggests that the NL is currently a bit more than 7 percent stronger than its counterpart.

Of course, that's just one possible permutation; we can apply the same procedure to reference leagues as far as 10 years back, as we've done in the table below. (To account for the fact that more recent data will be more reliable, we've taken the additional step of dividing the CPA by the number of years elapsed since the reference league completed play, which results in the weights provided in the table).

Reference League Weight (CPA/Years) Difficulty Ratio (NL/AL)
1993 NL 0.3% 1.060
1993 AL 0.8% 0.897
1994 NL 0.6% 1.008
1994 AL 1.1% 0.925
1995 NL 0.9% 0.905
1995 AL 1.9% 0.948
1996 NL 1.4% 0.946
1996 AL 2.9% 0.930
1997 NL 2.4% 0.934
1997 AL 3.7% 0.886
1998 NL 3.7% 0.950
1998 AL 4.2% 0.867
1999 NL 5.3% 0.929
1999 AL 5.8% 0.917
2000 NL 6.6% 0.857
2000 AL 7.6% 1.047
2001 NL 9.4% 0.929
2001 AL 11.2% 0.954
2002 NL 12.4% 1.002
2002 AL 15.8% 0.989
2003 NL 2.0% 1.216
Weighted average   0.957

Our ratio is set up such that a score less than one indicates that the NL is more difficult; using that standard, the NL came out ahead for 16 of the 21 reference leagues tested. Combining these results based on our weighting scheme, the advantage comes out to between 4-5 percent in the National League's favor.

What's interesting is that the 4-5 percent advantage described above jibes very well with the lopsided interleague results we observed earlier. If we combine a difference in league quality of that magnitude with the scheduling advantage that we described earlier, we'd expect the NL to have won about 53 percent of interleague contests, very close to the actual figure. The NL's advantage in interleague play may well have been real.

One final point: the evidence suggests that the NL's dominance is largely a new phenomenon. If we run the same analysis for seasons past, this turns out to be the first time since 1990 that the NL has rated as the stronger league:

Year Difficulty ratio (NL/AL)
2003 0.956
2002 1.003
2001 1.006
2000 1.029
1999 1.014
1998 1.080
1997 1.049
1996 1.048
1995 1.051
1994 1.043
1993 1.019
1992 1.055
1991 1.024
1990 0.992

The shift in league power has been quite dramatic. Throughout the late 1990s, the AL rated as at least four percent stronger, peaking at eigth percent better in 1998. Since then, the tide has shifted, moving fully in favor of the NL this season.

We've been on record many times as being critical of Bud Selig's claims of competitive imbalance, but this may represent at least a partial point in his favor. It might not be a coincidence that 1998, the year the Yankees won 125 games, represented the high-water mark in terms of the AL's strength. Since then, the presence of dominant AL franchises like the Yanks, Mariners and A's may have deterred other teams from competing, as they choose to pocket their revenue-sharing money or reinvest in their farm systems instead. With the possible exception of the Braves, the NL has lacked such juggernauts, and a higher percentage of teams have made a good-faith effort to compete in the near term, providing for superior depth.

Although we don't condone the behavior of teams like the Tigers or the Royals, or the incentives that revenue sharing has provided them to take the courses of action that they have, it's easier to sympathize with such strategies given the presence of a handful of elite franchises within their own league. Competitive imbalance, in other words, may have become a self-fulfilling prophecy of sorts, at least in the American League.

The great irony here is that the Yankees' very dominance may come back to bite them. By setting the bar so high, the Yankees have discouraged all but a few of the teams in their own league from attempting to compete with them. As a result, there's been a gradual migration of talent to the National League, the effect of which is that the NL has a better-than-even chance to win this year's Mid-Season Classic. If the Yankees lose Game 7 of the World Series in a closely fought contest at Turner Field or Pac Bell Park, they may have nobody but themselves to blame.

Well, and Bud Selig. Who said that a tie doesn't produce any losers?

You can check out more work from the team of writers of the Baseball Prospectus at

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