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TheGrandHatching Clears the Air

A number of recent conversations on this site (as well as Ducksnorts) have concerned the notion of the "Expected Win-Loss" (X W-L) differential, specifically in its capacity to predict the "Actual Win-Loss" (W-L) differential for any given team.  The formula itself takes into consideration how many runs a team has scored (Runs Scored, or RS), as well as how many it has given up (Runs Allowed, or RA).  The key assumption is that a team's W-L record is significantly correlated with its RS-RA differential.  Hence, a team that scores a lot of runs and gives up few should have a better record than a team that scores few runs and gives up a ton.  I doubt too many people would have a problem with this, especially given a large enough sample size (as Dex noted in a recent post).  In fact, I found out that at the end of the 2006 season the W-L for the league was very highly correlated with the X W-L numbers (r = .91).  Again, no big surprise.

The problem as I see it is that (1) the season is only 162 games, and (2) the division races are usually very tight (last year, 4 of the 6 division races were decided by 4 games or less).  In this case, over the span of 162 games, you would hope that the X W-L formula would have a margin of error less than that, right?  Well, as it turns out, if you look at the distribution of actual-predicted wins for the league in 2006, you would observe a standard deviation of over +- 4 games, which essentially means that only about 68% of the league would come within about +- 4 wins of their predicted totals (assuming a normal distribution - in reality, 53% of the teams came within 3 or fewer wins, and 73% came within 4 or fewer).  Roughly 95% of the league came within +- 8 wins.

Furthermore, the X W-L formula only predicted 2 of the 6 division winners.  And this is after the season has finished!  I can't even imagine what its accuracy was at the All-Star Break or the July 31st trade deadline when a GM might actually need this formula.

So what does all of this mean?  Well, while X W-L is certainly correlated to a high degree with W-L (no shit?), its value in the grand scheme of things is questionable at best.  I don't see how it could play a significant role in whether or not you pick up that "big bat" you've been eyeing, or in an evaluation of the "depth" of your bullpen.  As I see it, there's always room for improvement.

This FanPost was written by a member of the Gaslamp Ball community and does not necessarily reflect the views of the Gaslamp Ball managers or SB Nation.

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Pythagorean Record
Hardball Times had a nice article on it a couple months back.

by osbug on Jun 27, 2007 11:49 AM PDT   0 recs

Terrific article
Thanks!
"At the end, excitement maintained its hysteria." - Jerry Coleman

by TheGrandHatching on Jun 28, 2007 7:50 AM PDT to parent up   0 recs

how it might play a role
If your team is off the mark by several wins and losses, it would give you an indicator of how well off you actually are. Right now, our team's "unlucky". If our W-L record was actually much higher than expected, then Towers would be counting his blessings and desperately trying to figure out what's going on.

I think the other thing people have to remember is it's not like these numbers live in a vacuum. If the expected is off then it's not like that means we have to go and do something. We'd then take the next steps and compare ourselves to baseline figures and trends.

There is no magic number regardless of what anyone thinks they thought they read in Moneyball.

by Dex on Jun 27, 2007 12:34 PM PDT   0 recs

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