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Silly baseball example illustrates a couple of key ideas they don’t usually teach you in statistics class

- July 31, 2010

From a commenter on the web, 21 May 2010:

Tampa Bay: Playing .732 ball in the toughest division in baseball, wiped their feet on NY twice. If they sweep Houston, which seems pretty likely, they will be at .750, which I [the commenter] have never heard of.

At the time of that posting, the Rays were 30-11. Quick calculation: if a team is good enough to be expected to win 100 games, that is, Pr(win) = 100/162 = .617, then there’s a 5% chance that they’ll have won at least 30 of their first 41 games. That’s a calculation based on simple probability theory of independent events, which isn’t quite right here but will get you close and is a good way to train one’s intuition, I think.

Having a .732 record after 41 games is not unheard-of. The Detroit Tigers won 35 of their first 40 games in 1984: that’s .875. (I happen to remember that fast start, having been an Orioles fan at the time.)

More here.

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