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Monday, June 11, 2001

Manic Regression

Don’t worry. Voros isn’t coming clean about a hyperactive deterioration of his psyche. Not yet at least. Instead he’s written a little about Steve Trachsel’s trip to the minors.

It must have all sounded very convincing to Steve Trachsel.   “This is exactly the same idea we had with Bobby (Jones) last year,” opined   Steve Phillips, “to send him down and get him back on track.” All Trachsel had   to was to accept the assignment to the minors and the Mets would “fix” Trachsel’s   problems the same way they did with Bobby Jones. And they had proof too. Jones   was 1-3 with a 10.19 ERA before his demotion last year, and 10-3 with a 3.69   ERA after. Clearly the demotion had achieved its desired result.

And so another chapter in the annals of Post Hoc reasoning had been added.   At times, it seems that most everybody understands the pitfalls of “after this,   therefore because of this reasoning.” After all, if you drop your keys and find   a dollar bill on the sidewalk, you don’t spend the rest of the day walking down   the street dropping your keys every three seconds. However, there is a special   case of this reasoning that causes many people problems.

The principle of regression is a standard mathematical concept that has been   extended to elementary logic. Simplistically, the idea is that when two things   are imperfectly related (like past player performance and future player performance),   extreme values on one end match up with less extreme values on the other. We   see this in baseball very often and usually think very little of it. For example,   until recently very few players who hit 50 homers in one season, hit 50 again   the next. So that even though George Foster hit 52 Homers in 1977, while because   of that display we’d expect him to hit for power again, he shouldn’t have been   expected to hit 50 again in 1978. The Chicago White Sox of 2000 and the White   Sox of 2001 are another good example.

In the Mets example, we lack a key piece of information in the case of Bobby   Jones and how it relates to Trachsel’s situation. What we lack is the knowledge   of what would have happened if Jones hadn’t been sent down. The possibility   exists that he would have improved anyway. In fact, it was a probability   when you consider Jones previous performances and the principle of regression.   As in Trachsel’s case, Jones had an established level of ability that made his   poor performance in 2000 qualify as an extreme departure from his previous performances.   Isn’t it reasonable to assume that Jones would have improved even if the Mets   hadn’t done anything? Aren’t there dozens upon dozens of cases of that exact   thing happening? Even if you won’t go that far, doesn’t that possibility at   least exist? Why should we assume that being demoted had anything to do with   the turnaround.

You know, I could stand here and perform an ancient tribal dance to summon   the spirit of Dave   Bancroft and have it breathe life into the bat of Royce Clayton. Then, when   Clayton hits considerably better afterward than he had beforehand, I can declare   the ritual a success. I realize nobody will believe me, but if my results are   no less remarkable than those that Steve Phillips has achieved, why are his   methods “proven” and mine absurd?

And that lies at the heart of what is known as the “regressive fallacy.” We   as humans over the centuries have observed the principle that objects in motion   tend to stay in motion, and have developed habits and techniques for anticipating   and predicting future events. These generally valid techniques sometimes lead   us astray when analyzing out of the ordinary events. Therefore, when Troy Glaus   hits 47 Homers at 23 years old, people consider his current less ambitious pace   (17 homers in 60 games) a “disappointment.” If he hits 47 at 23 years old, he   should hit 49 at 24, 51 at 25, 54 at 26 and 58 homers at 27 years old, right?   Well, of course not. The list of 23 year olds who hit that many homers is woefully   small and none of them hit as many the following year so the expectation that   Glaus would do so is unfounded.

This misunderstanding of regression is at the heart of many questionable beliefs   in baseball. The belief in the supreme power of “team chemistry” is reinforced   when a team playing unexpected well adds a new player and then “suddenly” starts   playing worse. The player must have disrupted the team’s “chemistry.” A struggling   player gets moved to a new spot in the batting order and “poof” he starts hitting   again. It must be the new spot. A team losing more games than expected fires   its manager, then the team begins playing better for the new guy. Must have   “woken them up.” It isn’t to say any of those explanations are necessarily “wrong,”   just that they aren’t are as clear cut as they would appear, nor are the explanations   necessary to explain what happened.

Just once I’d like to hear Chip Caray say: “Rondell White’s 3 for 4 today.   You know, Jeff Pentland the Cubs’ hitting coach is trying to get Rondell to   relax his forearms at the point of impact in order to give him a more fluid   stroke through the zone. While Rondell has really hit the ball well today,   it seems to me that since Rondell’s been a career .290 hitter over several seasons,   he was gonna start hitting better than .230 regardless of what Pentland had   to say.”

But hey, what do Cubs fans care? As long as it works, why knock it? Right?

Voros McCracken Posted: June 11, 2001 at 06:00 AM | 3 comment(s) Login to Bookmark
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   1. Warren Posted: June 11, 2001 at 12:07 AM (#603894)
Certainly "post hoc" comments are used an almost insane amounts in sports, and Bobby Jones' performance last year is a good example - I'm not sure there was a definitive problem that was corrected in AAA - as you said, he regressed toward the mean as you'd expect. However, I think Steve Trachsel may be a slightly different case - supposedly he had been tipping his pitches, something that was corrected at AAA. Certainly, he'd probably improve after his return the majors anyway, since it's hard for *anyone* to sustain an ERA over 8, but I wouldn't say that his trip to AAA would necessarily be completely independent of a change in performance in Trachsel's case.
   2. Jason Posted: June 11, 2001 at 12:07 AM (#603897)
If read carefully, good statistical writing such as that found on this site and Rob Neyer never state absolutes. The point of the analysis is to find trends that help to explain player performance. Could anyone have predicted Brady Anderson's 50 HR season? Or how about the complete dominance of this year's Mariners squad? Of course not. You would have said that these things *probably* would not have happened but they *could* happen.

But why do things happen? Players have abilities that improve, decline, or stay constant. A myriad of factors go into player performance and those multiply to come up with team performance. It's just much easier for a club to say that a new player messed up a team's chemistry rather than to say that the team just hit a bad streak where balls didn't fall in for them. Teams must feel like they are in control of what is happening, whether they are or not.

No one denies that mechanics get messed up. If Greg Maddux suddenly turned into Paul Wilson, Leo Mazzone would figure out what was wrong and fix it. But using specious logic like the Mets' is just silly, and that is something that should be pointed out to make us more educated observers of the game.
   3. Jim Furtado Posted: June 12, 2001 at 12:08 AM (#603899)
It makes sense to send players to the minors for a short period when their mechanics get as out of wack as Traschel's did or when players need to work themselves back from injury. It's better to have them get cuffed around in the minors where bad performances don't impact the won/lost record of the Major League team. For example, the Red Sox would have been better served had David Cone made a few more starts at Triple A.

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