Monday, May 3, 2010

Gambler's Fallacy Fallacy?

I was intrigued by the title of this article by AJ Mass, but it turns out to not be very good. Mass correctly defines gambler's fallacy, and his large point -- that a hot or cold streak tells us little about a baseball player's future performance -- is a good one. However, he seems to be under the impression that gambler's fallacy means that all future outcomes are of equal likelihood, which is generally not the case at all. Despite his casino experience, he also does not seem to have a firm grasp on the law of large numbers. You often can predict a player's batting statistics with reasonable accuracy over long stretches of a season (and when you cannot, it usually has nothing to do with gambler's fallacy).

Mass also fails to point out the obvious concerning a recent Cincinnati Reds victory over Roy Oswalt, who was 23-1 in his last 24 decisions against them before the loss. Oswalt used to be an amazing pitcher on good Astros teams playing mediocre or bad Reds teams, and now Oswalt is a decent pitcher on a terrible Astros team playing a decent Reds team. It is not a fallacy on my part to say another loss to the Reds was likely.

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