2/05/19 DRC+ update- some partial fixes, some new problems

BP released an update to DRC+ yesterday purporting to fix/improve several issues that have been raised on this blog.  One thing didn’t change at all though- DRC+ still isn’t a hitting metric.  It still assigns pitchers artificially low values no matter how well they hit, and the areas of superior projection (where actually true) are largely driven by this.  The update claimed two real areas of improvement.


The first is in treating outlier players.  As discussed in C’mon Man- Baseball Prospectus DRC+ Edition by treating player seasons individually and regressing them, instead of treating careers, DRC+ will continually fail to realize that outliers are really outliers. Their fix is, roughly, to make a prior distribution based on all player performances in surrounding years, and hopefully not regress the outliers as much because it realizes something like them might actually exist.  That mitigates the problem a little, sometimes, but it’s still an essentially random fix.  Some cases previously mentioned look better, and others, like Don Kessinger vs. Larry Bowa still don’t make any sense at all.  They’re very similar offensive players, in the same league, overlapping in most of their careers, and yet Kessinger gets wRC-DRC bumped from 72 to 80 while Bowa only goes from 70 to 72, even though Kessinger was *more* TTO-based.

To their credit- or at least to credit their self-awareness, they seem to know that their metric is not reliable at its core for valuation.  Jonathan Judge says

“As always, you should remember that, over the course of a career, a player’s raw stats—even for something like batting average—tend to be much more informative than they are for individual seasons. If a hitter consistently seems to exceed what DRC+ expects for them, at some point, you should feel free to prefer, or at least further account for, the different raw results.”

Roughly translated, “Regressed 1-year performance is a better estimation of talent that 1-year raw performance, but ignoring the rest of a player’s career and re-estimating talent 1 year at a time can cause discrepancies, and if it does, trust the career numbers more.” I have no argument with that.  The question remains how BP will actually use the stat- if we get more fluff pieces on DRC+ outliers who are obviously just the kind career discrepancies Judge and I talked about, that’s bad.  If it is mainly used to de-luck balls in play for players who haven’t demonstrated that they deserve much outlier consideration, that’s basically fine and definitely not the dumbest thing I’ve seen lately.


This, on the other hand, well might be.

Mark Melancon 2011 1 1 -3 2 -0.1
Dan Runzler 2011 1 1 -17 2 -0.1
Matt Guerrier 2011 1 1 -13 2 -0.1
Santiago Casilla 2011 1 1 -12 2 -0.1
Josh Stinson 2011 1 1 -15 2 -0.1
Jose Veras 2011 1 1 -14 2 -0.1
Javy Guerra 2011 1 1 -15 2 -0.1
Joey Gathright 2011 1 1 81 1 0

Not just the blatant cheating (Gathright is the only position player on the list), but the DRC+ SDs make no sense.  Based on one identical PA, DRC+ claims that there’s a 1 in hundreds of thousands chance that Runzler is a better hitter than Melancon and also assigns negative runs to a walk because a pitcher drew it.  The DRC+ SDs were pure nonsense before, but now they’re a new kind of nonsense. These players ranged from 9-31 SD in the previous iteration of DRC+, and while the low end of that was still certainly too low, SDs of 1-2 are beyond absurd, and the fact that they’re that low *only for players with almost no PAs* is a huge red flag that something inside the black box is terribly wrong.  Tango recently explored the SD of wRC+/WAR and found that the SDs should be similar for most players with the same number of PA.  DRC+ SDs done correctly could legitimately show up as slightly lower, because they’re the SD of a regressed stat, but that’s with an emphasis on slightly.  Not SDs of 1 or 2 for anybody, and not lower SDs for pitchers and part-time players who aren’t close to a season full of PAs.

Park Adjustments

I’d observed before that DRC+ still contains a lot of park factor and they’ve taken steps to address this.  They adjusted Colorado hitters more in this iteration while saying there wasn’t anything wrong with their previous park factors.  I’m not sure exactly how that makes sense, unless they just weren’t correcting for park factor before, but they claim to be park-isolated now and show a regression against their park factors to prove it.  Of course the key word in that claim is THEIR park factors.  I reran the numbers from the linked post with the new DRC+s, and while they have made an improvement, they’re still correlated to both Fangraphs park factor and my surrounding-years park factor estimate at the r=0.17-0.18 level, with all that entails (still overrating Rockies hitters, for one, just not by as much).

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