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Friday, August 21, 2009Near-Sighted MarcelsPosted by John Burnson at 2:30amIn the sweep of human history, major-league baseball is, shall we say, a recent innovation. It’s not surprising, then, that we have a poor sense of the proper time scale for evaluating baseball talent. Only since a bunch of men met in La Rotisserie Française to draft mock baseball teams did what happened three years ago become more important to our survival than what happened yesterday. Take hitters. Tom Tango’s Marcel system says that a hitter’s expected performance in one year is a function of his (and his league’s) numbers in the prior three years. One element of the algorithm is a weighting of 3/12 for the hitter’s performance in the earliest of those three years. There is no way that fantasy leaguers credit 25% of a hitter’s expected performance in 2010 to his numbers in 2007. (In truth, the full weighting is less than 25% since Marcel also calls for 1,200 PA of league-average stats. However, 3/12 is the fraction of the hitter’s portion contributed by that early year.) Likewise, Marcel asserts that the latest of the hitter’s last three seasons contributes 5/12 (out of all the hitter’s numbers) to the next year. Propose to your leaguemates that less than 50% of a hitter’s expected performance in 2010 hinges on his play in 2009 and you’ll be laughed out of the room. But those are the ratios per Marcel (and I’m sticking with Marcel here, granting that it is simple, because “simple” can still mean “smarter than us”). The past is prologue, but the immediate past is not the whole story. The point is not that just-closed history is immaterial but that only slightly mustier history fades too fast. I don’t know about you, but six months ago feels like three years ago to me. What we would be really useful, for fantasy games, is a way to identify players for whom we have exaggerated perceptions—those are the rich buying and selling opportunities. One route would be to examine ownership levels in online leagues or aggregate rankings in mock drafts. However, simpler would be a programmatic approach. To that end, we’ve created Near-Sighted Marcels (NSM's). NSM’s are simply Marcels with a more, ahem, human-like ratio of memories. In Near-Sighted Marcels, the remote past still counts, but the recent past counts much, much more. What ratio of the past three seasons should we use? After careful (in human terms!) deliberation, we went with 80/15/5—that is, our internal projections for players are composed roughly of 80% of this year’s numbers, 15% of last year’s, & a sprinkling of the year before’s. That seems a fair (if humbling) allotment. (In the Comments, feel free to discuss the ratio that you would choose.) Here is a comparison of the coefficients for both standard and near-sighted Marcel (ratios adjusted to 100):
By this light, humans judge the immediate past to be twice as relevant as does Marcel, but the prior year only 1/2 as much, and the outlying year only 1/5 so. We generated both Marcels and NSM’s for 2010 for the current crop of hitters. We pro-rated the YTD numbers to a full season by multiplying by 4/3. We also expressed the ratio for NSM's as 9.6/1.8/0.6 so that the total magnitude (12) would be the same as with Marcels (5/4/3) and mesh with the injection of league-average PA. Let’s stick to OPS. We’ll define “Sentiment” as a batter’s NSM OPS minus his Marcel OPS (so a Sentiment above 0 indicates a player who is regarded more favorably by humans than by Marcel). The leader in Sentiment this year is Tampa Bay shortstop Jason Bartlett:
If you give this season a weighting of 80%, you anticipate an OPS for Bartlett of over 850. Now, Bartlett is having a stellar season, but Sentiment advises us not to get carried away by a guy who had a career 699 OPS in 1,700 PA entering this season, and who has hit as many home runs this season as he did for his entire career before 2009. Among players with at least 300 PA, here are the leaders in Sentiment:
Say what you will about their maturation (and you will say it), these guys should be regarded with a dash of skepticism and off-loaded (for top dollar) with only seeming reluctance. Every thing that can go their way, has. It’s harder to find laggards in Sentiment with more than 300 PA—depressed play usually means depressed playing time. Still, you could probably guess the big names: Giles, Ortiz, Cedeno, Ordonez, Renteria, Matsui, Upton (B.J.), Burrell, Atkins, Navarro. Guys who (as anyone is happy to tell you) are down to their last swings. If I had a rebuilding team, I would be scooping up these guys like souvenir cups (and at comparable prices). It’s good to take stock of our limits. It’s even better if we can characterize those limits and play against them. As you plan your keepers for next season, remember those ancient eras when the year ended in an "8" or "7." (Here is a link to a spreadsheet with both regular and near-sighted Marcels for all hitters with at-bats in each of the last three years.) Compiled by THT Staff.
Jonathan said...
Nice work. I assume the Mean-squared errors of the near-sighted version is worse? Posted 08/21 at 10:37 AM
John Burnson said...
Hill has only a +18 Sentiment. Although Hill had an off-year last year, he did so in only 205 AB. So that’s not overly held against him by regular Marcel. And Hill’s 2007 campaign (792 OPS) is in the same league as his 2009 campaign (832 OPS). It would be interesting if people have a harsher view of Hill’s 2008 than does Marcel—maybe we remember the rate stats well but not the playing time? Posted 08/21 at 10:39 AM
John Burnson said...
Jonathan—I didn’t even run them! I assume that standard Marcel is better. I would be worried if Near-Sighted Marcel turned out sharper…. Posted 08/21 at 10:42 AM
FreeZo said...
Zobrist If we are to discard players without 300 PA this year, why wouldn’t we discard those with fewer than 300 in 2007? Say what you want about 431 PA in 2009, hes closer to that than his 105 PA sample size of .391 OPS in 2007 and by a greater margin than the far-sighted Marcels would lead you to believe. Posted 08/21 at 12:58 PM
John Burnson said...
FreeZo- I limited the table in the article to guys with 300 PA because those are the ones who have contributed this year & made an impression. The spreadsheet includes hitters with less than 300 PA. Regarding Zobrist, as you note he has only about 750 PA over three seasons. That’s not enough for usual Marcel to get worked up, either up or down. This sort of gets back to my note about Hill. We may remember that Zobrist batted .253 last year and .155 the year before. But the sample sizes (in all three years) are too small to seriously conclude either that (1) Zobrist has matured or (2) Zobrist is a very good hitter. He MAY BE a very good hitter, and he MAY HAVE matured. But any such judgment rests on scraps (in the MLB data, I mean; minor-league data may say more). Posted 08/21 at 01:26 PM
Brian said...
Would like to see these two models tested for 2009 using 2006/2007/2008 as the input variables. Can anyone point to a comparable study such as this for zips/chone et al? Posted 08/21 at 01:50 PM
Derek Carty said...
Terrific stuff, John. This actually goes hand-in-hand with what I was saying last week about owners placing too much emphasis on current year stats, which some readers seemed at least a little skeptical about. Posted 08/21 at 02:09 PM
Dylan said...
I think the best comparison for this is between those 2, Hill and Zorbist, who do you think will get drafted earlier next year. Both 2b(Zorbist having OF and posibly SS in some leagues), both providing alot of power for a middle infield position, and around the same age. Zorbist does have a big advantage in SLG and OBP, but I bet most leagues will have Hill drafted first based on him having had a similar year in 2007(and ignoreing 2008), whereas Zorbist hasn’t really had one at all(But has improved each year), even though he would probably bring more value over a full season. Posted 08/24 at 01:53 PM
John Burnson said...
Good eye, Dylan. I bet it’s close, but I will be surprised if Hill is ranked over Zobrist. Hill’s numbers are nice, but Zobrist’s 948 OPS is 100+ points higher. And even standard Marcel—which, let’s be clear, isn’t BLIND to the most recent performance—prefers Zobrist to Hill. A lot depends on projected PT. The lesson here is probably to not have put too much stock in Hill’s drop in power in 2008. A 361 SLG is poor, but without the injury, Hill would have had 400 more AB to rebound. Posted 08/24 at 03:06 PM
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Its funny how there are 3 Jays on the list of overpreformers, but Aaron Hill isn’t one of them.