Get to Know: WPA/LI
WPA/LI (context neutral wins / game state linear weights): How many wins a player contributes to his team with the Leverage Index aspect removed, invented by Tom Tango.
Calculating WPA/LI: WPA is divided by LI for each individual play attributed to a specific player and then the WPA/LI for the individual plays is then added up to create WPA/LI for an entire season. This is considerably different then taking a player’s WPA and dividing it by pLI.
Why you should care: Unlike standard linear weights, WPA/LI does take into account the situation. So at times when a walk would be just as valuable as a home run, WPA/LI accurately weights the walk and the home run, where linear weights would still give .13 wins to the home run and the walk .03 wins.
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David,
I am extremely confused by this description. If WPA were “context neutral” than what would be the point or “removing” the LI aspect? Furthermore, aren’t we technically introducing a LI aspect by including it in the definition/equation? If I understand the stat correctly, it measures contextual (as opposed to wOBA’s inherent) value per opportunity to contribute, and a number closer to zero is worse. It’s be really helpful to include some “baselines”. Also, I understand that mathematically WPA/LI is different than WPA/pLI, but I have been unable to grasp the statistical significance of that fact. Thanks.