The Houston Astros are heading to the American League and baseball is headed toward balanced divisions (numerically at least) and 10 playoff teams. There are many fans in Houston upset at the move, but one aspect that they ought to consider being excessively happy about is the team’s improved playoff probabilities under the forthcoming new alignment.
Currently baseball is a mess of uneven odds. The squads in the AL West only have three foes to compete with for a division crown while the Astros and others in the NL Central have five each. Furthermore, American League teams only have ten others to battle with for the current single wild card spot. National Leaguers must outpace 12 others in the race for baseball’s second chance bracket. Between the years of 1995 (no playoffs in 1994 remember? Good thing the new CBA’s already done) and 2012, there were four separate probabilities for making baseball’s postseason depending on which division a team played in.
For the AL West and its four teams, each had a 31.8%* at the playoffs, assuming teams of equal strength. The AL Central and East division teams were next with a 27.2% chance. The NL West and East followed with a 26.2% and the NL Central teams bring up the rear at just 23.1%.
*Each team had a 25% chance at an automatic berth and then a 75% (since they can’t win both) chance at a wild card shot, which carried a 9% (1/11) probability. 0.25*1 + 0.75*1/11 = 31.8%. The formula comes from Bayes’ theorem.
With the switch to 15 teams per league, five teams per division and two floating wild card, every team in baseball will enter the season with identical odds. Again, assuming a theoretical model here in which teams are of equal strength. Going again to Bayes’ that probability is 0.2*1 + 0.8*2/12 or the same 33.3% chance you expect when five of 15, in equal set up, qualify.
Every team in baseball sees a boost in their chances to enjoy and reap the benefits of playoff baseball, but the NL Central teams, and their fans, have the biggest jump to celebrate.
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