I began the 2013 season with the pet theory that the NL Central would suffer as a result of losing the Houston Astros, while the AL West would gain. The Astros are historically terrible, and getting to play them often as part of your division meant you got a handful of gimme games per season.
So of course the exact opposite happened. The NL Central is sending three of its five teams to the playoffs, while the AL West is a sewer that fingers-crossed may be represented in the second wild card if the Texas Rangers do every single thing right in the final week.
Here are the stats, controlling for absolutely no other variables*:
Winning percentage/wins, NL Central
2012 w/o Astros: .503 / 395 wins (w/ Astros: .475)
2013: .520 / 416 wins
Winning percentage/wins, AL West:
AL West 2012: .543 / 341 wins
AL West 2013 w/o Astros: .519 / 332 wins (w/Astros: .479)
The five non-Astros teams in the NL Central won 21 more games in 2013 than 2012; the four non-Astros teams in the AL West won 19 fewer. We can thus describe the effect the Astros have on your division as a suck of 20 wins.**
At least they have an nice stadium.
* Blow me.
** Yes, a small sample size, but one would figure the teams are as similar as possible over two sequential seasons, thus setting up the closest thing we’ll ever have to a controlled experiment.