Birnbaum: A breakdown of the luck in MLB season records

From SABR member Phil Birnbaum at Sabermetric Research on April 25, 2013:

If you take a .500 baseball team, and flip it 162 times, you should expect it to come up "win" 81 times.  But that will vary -- sometimes it'll win fewer, and sometimes it'll win more.  You can calculate that the distribution of wins should follow a normal distribution, with a mean of 81, and a standard deviation of 6.36.

Using the rule of thumb that 95% of observations are within two standard deviations of the mean, you can figure that, around one time in 20, that team will win 94 or more games, or fewer than 68, just by luck alone.

Where does that luck show up?

The way I see it, you can break it up into five mutually-exclusive observations ...

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This page was last updated May 1, 2013 at 3:10 pm MST.