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The Problem with Win Expectancy
by Larry Mahnken

I've been sent a couple of Win Expectancy charts purporting to indicate that Ortiz is more valuable than A-Rod because of his clutch performance. There' s a couple of problems with this:

A) It doesn't account for defense. If a pitcher gives up a line drive into the right-centerfield gap, what would normally be an easy double or possible triple, and the centerfielder makes a fantastic running catch for the out, the pitcher is credited with an out, and all the Win Expectancy points. That overrates the pitcher, underrates the fielder, and gives an unfair advantage to players on the left side of the defensive spectrum. Some systems take points from a fielder for errors, which only increases the disadvantage some good defenders have.

Of course, more complicated systems account for the likely outcome of a ball in play by where it's hit, and credit the pitcher for that, and the difference between that and the actual outcome to the fielder who played it. None of the numbers I've been sent do that, but some teams, like the A's, have those numbers available in-house.

B) It doesn't account for replacement level. What would have been the Win Expectancy of the Red Sox if they had a replacement-level DH instead of Ortiz, or for the Yankees instead of A-Rod? Again, this is vital, because real value is not the change you make in the game, but rather the difference between the change you make and what the worst possible option would have made.

This also causes relief pitchers to be vastly overrated, because Win Expectancy changes much more rapidly in the later innings. This is because they are higher-leverage, and thus have a greater direct impact on the outcome of a game, but any pitcher would end up with a higher Win Expectancy in these innings. That they count more towards the game doesn't mean the player is better, or necessarily more valuable -- what would a replacement-level reliever do in that situation? The difference between that and what the reliever did is the reliever's actual value.

There are other problems, I'm sure, but these two in particular are a large part of the reason why WE rates Ortiz over A-Rod, when it shouldn't. Purely as a hitter, Ortiz appears more valuable than A-Rod, but they aren't purely hitters.

Someone emailed me to say that the voters never cared about defense, so it doesn't matter. Well, it does matter, because the rules of the MVP vote themselves define value, in part, as defense. We can now measure defense reasonably well, so we can determine the impact A-Rod's defense has on his value.

And just because voters ignored the rules in the past doesn't mean that they should. If A-Rod is the most valuable player in the league, then that's all there is to it. If the voters vote for Ortiz based on their past voting tendencies, ignoring defense and position, they still chose the wrong man. Making the same mistake many times does not make it no longer a mistake.

--posted at 3:08 PM by Larry Mahnken / |

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