Charlie Pavitt reviews a hitting streak study
I [Charlie Pavitt] am writing this in response to Trent McCotter’s piece on hitting streaks from the 2008 Baseball Research Journal. I want to begin by commending Trent on this fine piece of work. In short, a series of Monte Carlo tests revealed that the number of actual hitting streaks of lengths beginning with 5 games and ending with 35 games or more between 1957 and 2006 was, in each case, noticeably greater than what would have been expected by chance. It is always good to see evidence inconsistent with our “received wisdom.” What I have to say here in no way attempts to contradict his research findings. My problem is with his attempt to explain them.
Trent first proposed three “common-sense” explanations for what he found. The first was that a batter might face relatively poor pitching for a significant stretch of time, increasing the odds of a long streak. But, in his words (page 64), “the problem with this explanation is that it’s too short-sided; you can’t face bad pitching for too long without it noticeably increasing your numbers, plus you can’t play twenty games in a row against bad pitching staffs, which is what would be required to put together a long streak.” He then goes on (page 65) “The same reasoning is why playing at a hitter-friendly stadium doesn’t seem to work either, since these effects don’t continue for the necessary several weeks in a row.” His third “common-sense explanation” is that, as hitting overall is thought to be better during the warm months, hitting streaks may be more common than expected during June through August. This is because, and this is critical (page 65), “hitting streaks are exponential…a player who hits .300 for two months will be less likely to have a hitting streak than a player who hits .200 one month and .400 the next...[because]…hitting streaks tend to highly favor batters who are hitting very well, even if it’s just for a short period.” This is absolutely correct. Unlike the first two proposed explanations, in this case Trent looked for relevant evidence, claiming that he looked for more streaks in June, July or August and found no more than in May. Trent, how about April and September?
Anyway, rejecting all three of these, Trent then proposed two possible psychological explanations. The first is that hitters aware of a streak intentionally change their approach to go for more singles, particularly when the streak gets long; and he has evidence that longer streaks occur less randomly than shorter ones, which would occur under this assumption (players would more likely think about keeping their streak going when it was long ongoing). The second is that hot hands really exist, and his claimed evidence is that taking games out of his random sample in which the player does not start increases the number of predicted hitting streaks, bringing it more in line with the number that actually occurred. Makes sense; a hitting streak is easier to maintain the more at bats one has in a game. He proposes that this could reflect real life because managers would start a player proportionally more often when he was hitting well. True, but we should keep in mind that the same statistical effect for starting games would occur whether there is a hot hand or not. In other words, I don’t think his evidence is very telling.
I want to be very clear here about my position on this issue. I have absolutely no problem with the suggestion that players’ performance is impacted by psychological factors; I don’t see how they aren’t. My problem is with the way in which those suggestions are treated. If we are serious about sabermetrics as a science, then we have to meet the standards of scientific explanation. As esteemed philosopher Karl Popper pointed out in his now-classic 1934 book "The Logic of Scientific Discovery," if a proposed explanation for observations is impossible to disconfirm, then we can’t take it seriously as scientific explanation. This is my problem with Trent’s treatment. Let us suppose that rather than finding more hitting streaks than chance would allow, Trent had found fewer. He could then say that the reason for this is that batters crumble under the stress of thinking about the streak and perform worse than they would normally. If Trent found no difference, he could then say that batters are psychologically unaffected by their circumstance. The point is that this sort of attempted explanation can be used to explain anything, and given our present store of knowledge about player psychology they are impossible to evaluate. Again, Trent’s proposals may be correct, but we can’t judge them, so we can’t take them as seriously as Trent appears to.
In contrast, the first three proposed explanations can be disconfirmed, so we can take them more seriously. Trent claims to have disconfirmed the third, but we need to know about April and September. But the real issue I have is with his dismissal of the first two, because he did not apply the logic in their case that he correctly applied for his “hot weather” proposal. Let me begin with the first. A batter does not have to face a bad pitching staff in consecutive games for his odds of a hitting streak to increase. Let us suppose that a batter faces worse pitching than average during only 10 of 30 games in May and makes up for it by facing worse pitching than average during 20 of 30 games in June. We use the same exact logic that Trent used correctly for the “hot weather” proposal; his odds of having a batting streak, which would occur during June, would be greater than another batter that faced worse pitching than average during 15 games in May and 15 games in June. The same explanation goes for hitter-friendly and hitter-unfriendly ballparks, and is strengthened in this case because of well-supported known differences in ballpark effects. If a player’s home field was hitter-friendly and, during a stretch of time, many of his road games were in hitters’ parks, he could easily have 20 or more games in this context in a given month.
I have no idea whether either of these two explanations for Trent’s findings is correct. But the difference between these and his psychological proposals is that we could test these two and not those he favors. Given the importance of Trent’s original findings, I would obviously like to see that happen. And I would very much like it if we remain very careful about not taking our psychological speculations too seriously.