For example, if a hitter comes up with runners on first and second and two out in the bottom of the seventh inning of a tie game, his team has a 63% chance of winning. If that batter hits a home run, that percentage goes up to 95%. In this at-bat, this hitter had produced a WPA of .32.
Recently there has been more focus on WPA. The percentages above were calculated using this site. A couple years ago The Hardball Times' Dave Studeman wrote this fantastic overview of WPA. And there is even an entire site devoted to WPA- FanGraphs.
These sites piqued my interest in this statistic, but I found something missing. Stats like VORP and MLVr are adjusted for positions, but I had never seen this done with WPA.
I took the 2006 WPA statistics from FanGraphs, and sorted them by position. For each position, I then calculated the average WPA that came from an at-bat at that position. The results are as follows.
These results are pretty much in line with what I expected. I would have figured DH and 1B would be flip-flopped, but that is probably just an error caused by the small sample size. Later I will look at previous seasons.
The next step is to adjust actual WPAs using this data. My method of doing this was very simple- I took the player's at-bats multiplied by them by the per at-bat average for their position. Subtracting that number from their WPA gives us "Adjusted WPA".
Here are this season's current top 25 in unadjusted WPA, again courtesty of FanGraphs.
And here are the same 25 players, after their WPAs have been adjusted for their position. The final column is how far up or down their ranking has moved with this adjustment.
Not surprisingly, the order is significantly effected by adjusting for position. The middle infielders and catchers jump up the list, and corners fall back.
I plan on using seasons prior to 2006 fo make these adjustments more accurate, but I think these are pretty fair, and provide further insight to an interesting statistic.
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