Earlier this week, on the main FanGraphs blog, we re-ran Pizza Cutter’s classic study (yes, I think it’s a legitimate classic), 525,600 minutes: how do you measure a player in a year. In it, he demonstrated just how large of a sample size you really need before you can start drawing conclusions about a batter’s skills. The answer was a lot more than I think most folks realize: you can get an idea of a hitter’s swing % and contact rate pretty quickly, but stats like OBP, SLG, and especially AVG (much less BABIP!) take 500 PA or more to provide much useful information. While I think many fantasy managers understand the need for patience, I also see a tremendous emphasis placed on small samples when I read fantasy baseball advice–especially when it comes to players on hot and cold streaks.
Is there something special about a hot or cold streak that makes it different from a typical small sample of performance? It seems like there could be, right? Even if you can’t trust a normal sample of 20 PA’s, if someone is absolutely tearing the cover off the ball–or is striking out in virtually every PA–might that not mean that he’s likely to hit particularly well (or poorly) for the next few games? After all, we see (or, at least, think we see) guys go through amazing hot streaks all the time when watching baseball, and players describe what it’s like: the game slows down, the ball looks bigger, etc.
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