Category Archives: projections

PECOTA is probably wrong

This can’t be right.

Baseball Prospectus’ PECOTA league standings projection system came out today and it’s all over the blagoblag.

The projections, which twice correctly predicted huge jumps in the standings in 2008 for the Tampa Bay Rays and 2006 for the Chicago White Sox, had a very bad year last year and another bad year might cause people to look to other projection systems or maybe ignore the process.

PECOTA uses an intriguing system.  Started by SABR legend Nate Silver, it mapped every career ever had by any player in history and then applied those career arcs to the players with similar production–like I said in an earlier post, baseball is fortunate enough to have such an enormous sample size to take from.  From there, it extracted what the likelihood of the player’s production would be–10% (bad), 50% (average for him) and 90% (way above average).  Then it takes those player predictions, combines them into a team’s total run production (and prevention on pitching and defense) and voila! You have your pythagorian win-loss record.

One reason why PECOTA had such a bad year in 2009 wasn’t because of bad luck–PECOTA projections do not account for injury, trades or other things that come into play during a season–it’s because it projected inaccurately.* Even by pythagorian record, the A’s and Angels were swapped. The Indians and the Diamondbacks just plain old stunk. Craig Calcaterra pointed out PECOTA predicted one of the most amazing seasons in history by a rookie catcher for Matt Weiters and they were pretty far off.

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