The New Playoff Probabilities in 2013

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.





Matthew Carruth is a software engineer who has been fascinated with baseball statistics since age five. When not dissecting baseball, he is watching hockey or playing soccer.

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Flharfh
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Flharfh

Is there a way to account for, say, the Blue Jays having to play 3 good (Rays, Yanks, Bosox) and 1 terrible (O’s) team, while say, the Brewers have to play 2 goodish (Cardinals, Reds) and 2 terrible (Cubs, Astros) teams?

Flharfh
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Flharfh

Correction: Three terrible teams (forgot Pit)

Kyle H
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Kyle H

no this article is clearly not about the skill of a team. Over decades a teams current ability is negligible.

exxrox
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exxrox

unless we are talking about the Orioles or Pirates..oh wait, he was

TK
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TK

Or you don’t understand what “decades” means.

Toffer Peak
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Toffer Peak

Since 1976 (2.5 decades plus free agency started) the Pirates have a .472 record and the Orioles have a more respectable .492 record. NY and BOS kill at .570 and .544 respectively. So yes, even when looking at decades their are unfair divisions though the effect is often exaggerated and as noted in the long run it’s even smaller.

Kyle H
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Kyle H

Way to take the O’s best decade and cut it in half for that fact. Since 1960 they have 3 WS rings to Boston’s 2. And the AL East, or any division, has changed since then. The same Phillies in perennial contention were the first team to 10,000 losses in any sport. Yes the yankees are the yankees but beyond that you can’t tell me you have any clue who the good teams are in a decade.

Toffer Peak
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Toffer Peak

My reasoning was simple. That is the year MLB free agency began and it has dramatically and irreversibly changed competitive balance (barring major changes to the CBA and/or US legal decisions).