Wednesday, October 19, 2011

Baseball's World Series, which begins tonight, features two very hot teams. It's not just the relative ease with which the St. Louis Cardinals and Texas Rangers dispatched their respective rivals in the first two rounds of the playoffs, but also how the Cardinals and Rangers ended the regular season.

At the conclusion of play on August 24, the Cards were only slightly above .500, with a record of 67-63, hardly suggestive of a team that would become the National League representative in the Fall Classic. However, the Cardinals got hot for roughly the last month of the season (winning 23 games and losing only 9, to finish 90-72) while their rivals for the last playoff spot, the Atlanta Braves, got cold over the same period of time (11-21, including 6 losses in their final 7 games) to finish 89-73.

The American League champion Rangers finished the season even hotter than the Cardinals, winning 14 of their final 16 regular-season games to finish 96-66. Texas really fattened up on the worst teams in its division, going 15-4 vs. Seattle and 13-6 vs. Oakland in the regular season. However, any concerns about whether the Rangers could win steadily against better opposition were allayed in the initial playoff rounds, as Texas defeated Tampa Bay 3 games to 1, and Detroit 4 to 2.

Although it's guaranteed to happen this year, teams finishing the regular season on fire usually don't win the World Series. According to a 2005 study:

In the 35 years from 1969 through 2004, the team with best overall winning percentage won the World Series only eight times. Let me emphasize: the team with the best regular-season record has won the World Series only 23% of the time...

How about the teams with the best September record? The answer is exactly the same: they won eight World Series, too. Same impact. In six of the eight examples, however, the team with the best September record was also the team with the best overall record. So there's a lot of overlap between the two groups.

In fact, in about half of the last 35 years (17, to be exact), the team with the best regular-season record was also the team with the best record in September. Of those 17 teams, six won the World Series. Even teams that were Good and had Momentum won it all only 35% of the time.

 This 2006 article elaborates on why late-season hotness or coldness is not necessarily indicative of postseason performance.

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