SABR

Studeman: Talking about situational wins

From SABR member Dave Studeman at The Hardball Times on June 3, 2014:

I am totally fascinated by WPA/LI, even though I can’t really tell you what it is. The title says what it is: Win Probability Added divided by Leverage Index, but that doesn’t really help. We are probably better off calling it Situational Wins, which is a less geeky name for a very geeky concept. I tried my best to describe Situational Wins in this article (see the end), in which I called it “a number that indicates who ‘won’ the at-bat, and by how much.” Hence, the name. Situational Wins.

A vague explanation isn’t the only issue with Situational Wins. Here are some others.

  • Some people just don’t like WPA, and using WPA/LI (which corrects some of the things people don’t like about WPA) feels like jumping further into the rabbit hole.
  • Total WPA/LI for a team doesn’t equal the team’s won/loss record. WPA does (which is one of WPA’s main attractions).
  • Because of rounding and the infrequency of some situations, you sometimes get results that are a bit off.  I’ll show you a couple of examples below, but these small differences shouldn’t make much difference for players over the course of a season. Still, they exist.
  • WPA/LI is calculated by comparing two tables that Tangotiger has derived: WPA and LI by situation. We all trust Tango,  but are we certain his tables are completely correct?
  • WPA/LI has a bias in favor of home runs, because not all baseball events are randomly distributed across situations (personally, I don’t think this is a bias; it’s just a fact.  But I thought I’d mention it.)

Having said all that, my intuition is that WPA/LI works. To me the proof is in the postseason scenario (as described in my previous article) in which the added “championship value” of winning a game has a constant relationship to its leverage index. As a result, when you divide each game’s championship outcome by its leverage index, you get the same number.  Each game is equal in importance. Really, read the article.

Situational Wins do the same thing to plate appearances.  They ensure that each plate appearance is treated the same as every other plate appearance regardless of how important it is to the game.  The result is a measure of how successfully the batter or pitcher approached the situation.

Read the full article here: http://www.hardballtimes.com/talking-situational-wins/

This page was last updated June 3, 2014 at 10:50 am MST.

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