The Best of Leagues, the Worst of Leagues

As with every year, there have been storylines that are unique to the 2015 baseball season. The remarkable infusion of young talent to the game. The relevance of the Cubs and Astros after years of being doormats. The disarray in Boston and Detroit. And, of interest here, the general ineptitude of the American League.

Many commentators have bemoaned how weak the American League is this season. You can get a sense of that by just perusing the standings. All data here are as of the start of play on Sunday, September 6.

  • The Red Sox, Mariners, Tigers, White Sox, and A’s–all expected to be good teams this year, picked by many to win their divisions or qualify as wild cards–have the five worst records in the league.
  • Two divisions have only two clubs with winning records, and there are only six teams in the entire league more than a game above .500.
  • In the East, Toronto’s gotten hot, but the team had a losing record as recently as July 28. The Yankees’ two best offensive players are old, one’s hurt, and the other has the second-lowest OPS in the league in over the past 30 days. Nobody else in the division is above .500.
  • The Royals lead the Central with the American League’s best record despite having the fourth worst starting pitcher ERA and FIP along with, this being the Royals, the fewest home runs and walks on offense. The second place Twins have been outscored. Again, nobody else in the division is above .500.
  • The National League West is led by the Astros, a year after losing 92 games and two years after losing 111. Many of the players in their lineup have an on base percentage below .300 with the team. The Rangers are in second after losing their ace pitcher in spring training. The defending divisional champ Angels are treading water, just a game above .500.

Given that, one could argue that at least four of the best teams in baseball this year are in the National League, though one would get a counter-argument emanating along the Missouri/Kansas border. In any case, the Cardinals have the best record in the majors, the Pirates and Cubs third and fourth, the Dodgers tied for fifth, and the Mets eighth. The National League has the best teams, with the best records, making it the best league, right?

Except for one number: 89-73.

That’s roughly equal to the projected won-lost record for the Mets and Astros this year. That’s a good record. It’s good enough to win a soft division, good enough to make the playoffs in almost every year. An 89-73 team is a good ballclub.

But I didn’t list the 89-73 record because of the Mets and Astros. Rather, it has relevance for another reason: 89-73 is the record of American League teams against National League teams this year. Actually, it’s 151-123, but prorated over 162 games, it’s 89-73. The American League, on average, is the Rangers or Nationals playing against the Orioles or Red Sox: A .525 team playing a .475 team. The American League is, overall, clearly the superior league. And this shouldn’t come as a surprise; as Jeff Sullivan pointed out last year, the same occurred in 2014. And it happened in 2013. And 2012. And 2011. And every single year beginning in 2004.

How can that be? How can the top of the American League be unimpressive, the rest of the teams deeply flawed, yet the league is easily beating up on the National League?

There are two reasons. First, the National League may have the best teams, or at least most of them, but it absolutely runs the table on bad teams. The worst record in the majors this year is owned by the Phillies. They’re followed by the Braves. Then the Reds. Then the Marlins. Followed by the Rockies. The A’s are the next-worse, but then we return to the National League, with the Brewers. Six of the seven worst teams in the majors this year are in the National League. Those six teams, cumulatively, are 334-478, a .411 winning percentage, and 38-72 against the American League.

The second reason, closely related to the first, is parity. Yes, the American League doesn’t have the talented teams that the National League claims. But neither does it have the clunkers.When it comes to team performance, the National League is a stars-and-scrubs, penthouse-and-outhouse type of league. The American League is much more egalitarian. The teams with the six worst records in the American League are the A’s, Tigers, Red Sox, White Sox, Mariners, and Orioles. Those are six hugely disappointing teams, but they’re disappointing because they have talent, if underperforming talent. Those six teams, cumulatively, are 376-434, a .465 winning percentage, and 56-54 against the National League. Compare that to the six listed in the last paragraph.

Put this another way: You probably remember the term standard deviation from statistics classes. Without getting into the formulae, the standard deviation is a measure of variance. Given a normal distribution, about two-thirds of values (68.2%, to be precise) fall within one standard deviation of the mean. It’s a more precise term for “plus or minus.” Since 1998, the inaugural seasons of the Tampa Bay Rays and Arizona Diamondbacks, there have been 30 major-league teams. During that time, the average team won/lost percentage is .500 (duh). The standard deviation is .071. Over the course of a 162-game season, then, the average number of victories is 81 games (162 x .5), with a standard deviation of 11.6 games (162 x .071). If there’s a wide variation between teams in a league, its standard deviation will be higher. If there’s parity, it’ll be lower.

I calculated the standard deviations of team winning percentage for every season in each league from 1998 to 2015, giving me 36 league-seasons in total. I multiplied the result by 162 to express it in games. Again, in those 18 years, the average team wins 81 games, plus or minus 11.6. Here are five the seasons with the greatest standard deviations:

       Year   Lg    SD
       2002   AL   17.1
       2001   AL   15.9
       2003   AL   15.8
       1998   NL   14.3
       2004   NL   14.0

The 2001-2003 American League was the most unequal since 1998. The Mariners, with 302 wins in 2001-2003, including 116 in 2001, led the league in wins over the three seasons, which also featured outstanding teams in Oakland (301 wins) and New York (299). On the other side of the coin, Baltimore (288 losses), Tampa Bay (305 losses), and especially Detroit (321) were perennial doormats. This year’s National League, to date, is close to breaking the top five. It has a standard deviation of 13.2 games, which ranks eighth among the 36 league-seasons. It’s been a year of inequality in the Senior Circuit.

At the other extreme, here are the five seasons with the lowest standard deviations:

       Year   Lg    SD
       2015   AL    7.8
       2007   NL    7.9
       2006   NL    8.0
       2000   AL    8.7
       2005   NL    8.8

The 2005-2007 National League had only one team win 100 games (the 2005 Cardinals) and only one lose as many as 96 (the 2006 Cubs). In 2007, every team had between 71 (Giants and Marlins) and 90 (Diamondbacks and Rockies) wins. But that level of parity doesn’t match the 2015 American League so far. This year’s American League is on pace for the most egalitarian distribution of wins and losses in the 30-team era. It’s Sweden to the National League’s Honduras! Or something like that.

So what’re the takeaways? The record level parity in the American League to date has smoothed out the top and bottom of the league, resulting in hardly any notably bad or notably good teams. But that parity shouldn’t be mistaken for weakness. The American League is the better league overall, as evidenced by its clearly superior record in interleague play. The National League may have the best teams, but the American League remains the best league.

Writer for Baseball Prospectus

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Very cool stuff! FYI the second table says 2015 NL when it should be AL.


Variance is really not that hard a concept, except we really don’t teach it well, at least in the U.S. You have data, you can graph it as a histogram (another weird sounding word!).

The shape the data takes is important. The spread in AL wins looks “wider”.

K, that’s my rant against American education improperly placed in a Fangraphs article, but I’m rather drunk and mad and the underperforming A’s for almost getting perfecto’d by Colby friggin Lewis.

Great read, weird season.


“But that parity shouldn’t be mistaken for weakness.”

A concept lost in the college football world.

Mike Pozar
Mike Pozar

Is the statement “This year’s American League is on pace for the most egalitarian distribution of wins and losses in the 30-team era” accurate? If the SD is currently 7.8, as quoted, wouldn’t that be expected to increase as more games are played, thus putting them on pace to go past the next runner-up at 7.9?

OTOH I see in a comment that it’s actually decreased to 7.3 since the original post, so maybe now it will indeed set the most-egalitarian record 🙂