Has the AL Central been good or lucky?

How many pennants has each American League division won since the current three-division format began in 1994? Unless you’re pretty young, your mental model of the subsequent AL pennants reads like a Monty Python spam menu: East, East, East, East, someone else, East, East. Can’t we just have someone else without the East? Well, that’s essentially what’s happened since 2010, with the Rangers, Tigers, Royals, and Indians combining to take six of the last seven pennants. The Central in particular has won four of the last five pennants. So what’s going on? Is this just statistical variation in a weighted random-number generator?

I decided to put this in graphical terms, since humans are so good at (and so amused by) looking for patterns, real or otherwise. Below, I’ve graphed three winning percentages for each AL division since 1995 (all raw data from Baseball-Reference): the best & worst teams in each division, and the division average. For reference, I’ve also marked that year’s pennant winner, though that team hasn’t always had the highest regular-season w%.

To look at this another way, here are the total division averages for that period (high, average, low). Royals fans will not be surprised to see the AL Central seeming a bit weak compared to the other two:

But has the Central gotten better recently? It’s now taken 4 of the last 5 pennants, after all. But it’s not clear that anything has changed collectively; when you compare averages of the last 5 years to averages since 1995, at most you see a trend toward mediocrity:

AL Central average w% (best, avg, worst)

Last 5 years: .568, .493, .410

Last 22 years: .578, .492, .396

Of course, w% isn’t the only way to measure success (just ask those poor 2001 Mariners). How has the AL Central done getting its teams into the playoffs, and into the WS? Since 1995, the AL East has earned the Wild Card spot 16 times, compared to 2 for the Central and 4 for the West (I’m counting only the winner of the WC play-in game for these purposes). That’s 38 total playoff teams from the East, compared to 24 for the Central and 26 for the West.

In theory, that gives the East an overwhelming advantage; it’s had twice the entrants of either rival division 72% of the time since 1995. But the East has only won 11 pennants, half the total possible. From this angle, the Central looks pretty good, its teams winning the pennant about 1/3 of the time (including both its Wild Card entries), while the “dominant” East has lost more than its fair share compared to its total playoff teams, and the poor West just looks pathetic. Of course, until 2013 the West only had four teams, but that’s no excuse for being the playoff equivalent of William Jennings Bryan.

So what’s going on? If I’d done this project just a few years ago, the picture would have been very different, with the East looking dominant and the Central and West both whimpering for table scraps. To my eyes, it looks like increased parity. We haven’t seen dominant AL teams like the 1995 Indians or 1998 Yankees or 2001 Mariners in 15 years now, and there are fewer truly awful teams, too. The division averages are all hovering collectively around .500, not showing any real trends beyond what look to me like natural cycles.

Personally, I think the Central’s recent success is just a natural adjustment in the flow of baseball, possibly influenced by more parity. Three of the Central’s recent four pennants were won by teams without the best record in the league. With fewer dominant teams, it’s just more likely that the skewed numbers of the previous era will start to even out. That said, I don’t know what’s going on with the West, but in the next five years I wouldn’t be surprised to see that aberration start to resolve itself, too. Sometimes randomness is just that. After all, if the A’s and Astros hadn’t succumbed to #RoyalsDevilMagic for a couple innings, we could be talking about the AL West’s recent dominance.

This all reminds me of Stephen Jay Gould’s famous essay on the disappearance of .400 hitting in baseball, in which he essentially argued that the collective improvement of players was eliminating outliers. Paradoxically, yet logically, as players collectively become better it’s harder to remain outside the curve and standout performances tend to fade away. I suspect the same pattern is manifesting itself between teams and divisions.

One major factor I haven’t addressed is salary and spending: has something changed financially throughout the league, or in the Central, to influence recent events? That’s something I’d like to follow up on in a future piece. But in the meantime, I don’t think the Central has gotten particularly better in the last 5 years; it’s just responded to a broader pattern in baseball that includes increased parity and better analytics.

As a Royals fan, I’m quite grateful for this pattern, but I don’t think it has any larger meaning. What do you think?