March 1, 2012

BP Unfiltered

PECOTA and Depth Chart Update *UPDATED*

by Rob McQuown

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Sometimes, when you realize you've stepped in something malodorous, there's nothing to do but pause and deal with the situation at foot. Keep walking, and the substance will remain on your shoe, where it will begin to attract unwelcome attention. We made a similar misstep, in a proverbial sense, with some of our PECOTA projections this season. Recently, we discovered that National League pitchers were projected to be substantially worse than PECOTA’s logic intended due to a bug that slipped past our testing.

As unpleasant as removing the offending substance from your footwear can be, there’s always reason to be glad when it’s gone. In our case, that reason is the increased accuracy of our projections. While Clayton Kershaw still isn't projected to lead the league in WHIP—his past control problems still count against him, as Colin proved they should, so PECOTA isn't quite as wowed by his recent greatness as you or I might be—he is now projected to have the fifth-best ERA among qualifiers. You’ll find that virtually all other NL pitchers have seen their stats improve as well.

We’ve made one other big change that wasn't really a “bug fix” but will impact anyone who looks at the Depth Charts. For years, people have wondered why the team AVG/OBP/SLG projections weren't really in line with what teams ended up hitting, especially in the National League. The answer has always been that we've excluded pitcher hitting from these projected rate stats, while incorporating it into our team runs scored and allowed estimates. Well, we've changed our minds and added pitcher hitting to the team totals. So, sharing some of the pain I endured while writing about Astros players for BP2012, I'll inflict their projected season batting line upon everyone:

AVG/OBP/SLG (TAv): .248/.304/.371 (.243)

Considering Houston hit just .258/.311/.374 in 2011 and shipped out some major contributors (Hunter Pence and Michael Bourn, mainly—there weren’t that many major contributors to begin with), that projection seems entirely reasonable, much to the dismay of Astros fans.

Oh, and that number in parentheses? We added TAv to the slash lines while we were at it. (Before we added the pitchers in, the TAv values didn't make sense, as almost all of them were above the .260 mark.)

And for more fun with Depth Charts, there's a new "Visual Depth Chart" page, inspired by Ben Lindbergh's article on position weaknesses around the league.

We also made some other improvements in this PECOTA run that will be reflected soon on the player cards, and for now in the downloadable spreadsheet (click on “manage profile”), Depth Charts, Player Forecast Manager, Team Tracker, and the new Scoresheet Draft Aid. Among them are:

• A downgrade to many player FRAA values, which were being calibrated against historical values and coming in a bit too high.
• A fix for a minor bug in stolen base projections. I noticed this while writing about Nyjer Morgan for Value Picks a while back—it turns out PECOTA was over-counting steals in seasons where a player played for multiple teams, as Morgan did in 2009, and the smart readers picked up on that before I could quickly fix the problem and sweep it under the rug. (Just kidding—we'll continue to keep you posted when we change things, as we’re doing with this post.)
• A bug fix in pitcher WARP calculations that was originally fixed during the 2011 season but wasn't propagated to the earlier PECOTA runs. It’s in there now, so some pitchers will see a change in their WARP.

Writing this sort of “confessional” isn't much fun, but we at Baseball Prospectus do think that being open about such things is only fair to you, our readers. We hope that you’ll enjoy the improvements in the stats now that the fixes are in place. Meanwhile, we're paying even closer attention to where we step.

UPDATE TO THE UPDATE: Two more quick changes to tell you about. First, we've switched from using 2011 positional adjustments to using positional adjustments generated from the projected data in the depth charts themselves. Secondly, we've changed the weights on stolen bases and caught stealings to better reflect the run environment currently. --CW

Rob McQuown is an author of Baseball Prospectus. Follow @robmcquown
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