August 26, 2015

DRA Run Values

An Introduction

by Jonathan Judge

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Deserved Run Average (DRA) is, as you know, the new pitcher-value metric here at Baseball Prospectus. DRA reflects our best estimate of the runs each pitcher "deserved" to allow in a given season. The number of deserved runs above or below average is used to calculate BP's pitcher Wins Above Replacement Player (WARP).

By popular demand, we've now extracted the estimated effect, in runs, that various external factors have had on individual pitchers. You can get a direct link from the main site by clicking "DRA Run Values" from the Statistics pull-down menu, or by clicking here.

Overall feedback on DRA has been very positive, and we expect these run values will provide even more insight into the challenges various pitchers have faced. In other words, rather than simply knowing that DRA takes into account things like score differential and temperature, you can now see for yourself how those components have affected (or not affected) individual pitchers.

From the Run Values page, you'll learn that Zack Greinke has benefited from terrific catcher framing, but also dealt with poor defense. You'll see that his teammate, Clayton Kershaw, has lost about nine total runs from factors beyond his control, and that Dallas Keuchel has grabbed six free runs, largely from the parks in which he has pitched. You'll also see a glossary on top of the entire table that briefly explains each column.

There are always caveats. Here are some.

First, this table does not contain all of the external factors that DRA considers, just the ones most likely to be of interest. The table is a bit crowded as it is, and we want to keep things readable. The "adjusted runs" column at the far right gives you the total effect of the factors in the other columns in the table. Are there other adjustments accounted for in the model? Yes. If one of them interests you particularly, feel free to ask below.

Second, don't be surprised if some component run estimates diverge from other sites' predictions. Remember that DRA calculates its own estimates for each factor, on a season-by-season basis, in light of the other considered factors. Thus, DRA doesn't calculate generic park factors; rather, it calculates park factors that are adjusted for the temperature of the games played, the size of the strike zone there, and the quality of the teams that visited, among many other things. This doesn't mean you can't have your own opinion on these issues, or appreciate other perspectives, but it does mean that if DRA disagrees with somebody else about the effect of some component, it probably has a (uniquely) good reason for doing so.

Third, although we describe these figures as the "DRA Run Values," they technically are the "value" mixed-model results from the first step of DRA. Those who enjoy the details may recall that we typically subject the value-model derivations to a second step, the MARS model, to give each season's model the opportunity to consider basestealing prevention and other factors.

For this exercise, doing so is more trouble than it is worth, because the only factors DRA's 2015 model selected as relevant were (1) pitcher value, (2) volume of batters faced, and (3) the starting-pitcher percentage. None of the baserunning stats were deemed relevant to assessing league-wide pitcher run prevention for 2015 (or 2014, for that matter). Thus, the MARS model in recent years largely just filters out the effects of plate appearances and converts the raw-value numbers to runs allowed per nine innings (RA/9). Those are both important, but neither is helpful when simply looking at total pitcher run value.

Lastly, for now we've posted run values for pitchers from the 1998 through 2015. We'll push it back eventually to past seasons, and it's not particularly difficult to do so, but we wanted to get you the most recent ones now.

As always, let us know what you think. We think you'll have fun with these and get a much better sense of which areas constitute team strengths or weaknesses, and how it is that pitchers—even pitchers on the same team—can end up facing very different challenges.

Jonathan Judge is an author of Baseball Prospectus. Follow @bachlaw
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