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.
When you actually study hot and cold streaks empirically, however, it becomes hard to find much signature to the data. I wrote about one anecdotal case last week. In that article, I referenced Tom Tango and his coauthors’ study in The Book: Playing the Percentages in Baseball, which demonstrated that there is little predictive power to a hot or cold streak. I thought that today, I might recap their study for those who haven’t read it.
The methods were simple. From 2000-2003, any five-game streak in which an individual hitter had greater than a .525 wOBA was included in a batch of “hot streakers.” And any hitter with a wOBA over 5 games of .195 or under was placed in a bucket of “cold streakers.” Note that a player could have had a 6-game streak or 7-game streak and still be included–their methods just select five consecutive hot games by a player, regardless of what happened in game 6.
Actually, what happened in game 6 is ultimately the interesting thing: if hot streaks and cold streaks are predictive, you’d expect that players in these crazy-hot and crazy-cold streaks would continue to be at least somewhat hot or somewhat cold in their next games. Here’s what happened:
During the streak: .587 wOBA
Expected wOBA (just a 3-year average for the players): .365
Actual wOBA in game after streak: .369
Actual wOBA in five games after streak: .369
During the streak: .151 wOBA
Expected wOBA (3-year average again): .336
Actual wOBA in first game after streak: .330
Actual wOBA in five games after streak: .332
So, is there anything predictive about hot and cold streaks? Yes, there is…but it’s slight. If you pick up an insanely hot player, or bench an insanely cold player, you get about 5 points of wOBA (a bit less than 5 points of OBP) of predictive power. 5 measley points! This is quite frankly worthless in terms of making fantasy baseball decisions. You’ll do far better relying on a player’s overall talent than trying to catch a hot streak or avoid a cold streak–because chances are, by the time you react, it’s already over.
There’s one caveat I’ll add, however, from a fantasy perspective: predictive or not, real baseball managers look at hot and cold streaks. And even though they are generally not predictive, managers will give a guy more PT when he’s “hot.” The perfect example of this is Jed Lowrie, who had an insanely good week that, apparently, at least for now, has resulted in him securing the Boston starting SS job. Does Jed’s hot streak mean anything about his performance over this coming week that is different than if he’d hit like a normal human? Probably not–except that he now has a job (and maybe we bump up our estimate of his true talent level a couple of zots). Of course, a bad cold streak could reverse all of that pretty quickly…
For more on this topic, I’d highly recommend The Book. A major portion of what’s in there is directly applicable to fantasy, so it’s worth the read for that reason alone.