BDD: What PECOTA Says

At Baseball Daily Digest, I explain the aim of PECOTA:

Angels fans are irate that PECOTA predicts the team to win a mere 76 games. If we go to two standard deviations, between which data falls 95% of the time, the win range spans from 64-88.

“Great,” you say. “Even I could predict the Angels to win between 64-88 games.”

It seems trivial, but that is because people are expecting PECOTA to make grand claims when it’s really not going to do that. If you’re expecting PECOTA to mimic Nostradamus, you are always going to close your Internet browser disappointed.

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2 comments

  1. TheOptimist

    January 29, 2010 11:41 PM

    And you yet again ignore the point that if you’d bet on the Angels to be within the standard deviation of their PECOTA projection every year for the past 6 years (a span of 12 possible records) you’d have been wrong 6 years in a row, always in the same direction. Eventually, hitting that 32% chance (or the 5% one, as they did last year) stops being luck.

  2. Bill Baer

    January 30, 2010 08:46 AM

    So you’re saying if you roll a die and hit a 5 a few times in a row the die is unfair?

    Generally speaking, anything outside of three standard deviations is considered an outlier.

    1 STDEV = 68%
    2 STDEV = 95%
    3 STDEV = 99.7%

    That something is outside of one standard deviation isn’t anything remarkable.

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