Expected Win-Loss Record (X W-L)

Major League Baseball now posts (since mid-2006) a new stat:

X W-L – Expected won-loss record based on runs scored (RS) and runs allowed (RA), using this formula: RS^1.82/((RS^1.82)+(RA^1.82))

… what does this tell us?

Seemingly this stat can tell you how teams win, if the X W-L ratio greater than the actual W-L ratio the team loses close games but wins big, or if less than the team is winning close but losing big.

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for the real math behind it, check out this 1999 article form Baseball Prospectus

In practical terms, the implications are fairly small. For most off-the-cuff calculations of runs and runs allowed into wins, the 1.5% gain in accuracy isn’t worth the trouble of finding a new exponent for every team; just use 1.85 or thereabouts, and get on with your life.

It really makes a difference, though, to the small group of people who try to assess the value of a player’s performance as precisely as possible.

The most noticeable impact is going to be on the value of good pitchers in extremely pitching-friendly environments. A pitcher-friendly environment brings down the exponent; a good pitcher, by his own efforts, decreases the run environment and the Pythagorean exponent even further.

continue on for a good Bob Gibson example

Honestly, I don’t see how this helps anyone understand anything.

[tags]MLB, baseball, stats, X W-L[/tags]