Win probability added
Win Probability Added is a technical baseball statistic which attempts to measure a player's win contribution by figuring how much each specific play he made altered the outcome of a game.
Some form of Win Probability has been around for about 40 years; however, until computer use became widespread, Win Probability Added was often hard to figure or imprecise. With the aid of
Retrosheet, however, Win Probability Added has become substantially easier to calculate. The Win Probability for a specific situation in baseball (including the inning, number of outs, men on base, and score) is obtained by first finding all the teams that have encountered this situation. Then the winning percentage of these teams in these situations is found. This probability figure is then adjusted for home-field advantage. Thus Win Probability Added is the difference between the Win Probability when the player came to bat and the Win Probability when the play ended.
Win Probability and Win Shares
Some people confuse Win Probability Added with
Win Shares, since both are technical baseball statistics that attempt to measure a player's win contribution. However, they are quite different. In Win Shares, a player with 0 Win Shareshas contributed nothing to his team; in Win Probability Added, a player with 0 WPA points is average. Also, Win Shareswould give the same amount of credit to a player if he hit a lead-off solo home run that turned out to be decisive as if he hit a walk-off solo home run; WPA, however, would give vastly more credit to the player who hit the walk-off homer.
The Hardball Times
* [http://live.protrade.com/ PROTRADE Live]
* [http://www.fangraphs.com/ Fan Graphs]
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