There was a comment that was posted yesterday on the post "Did the Giants' Front Office Make the NL West Race Closer Than it Needed to Be?" that got me thinking. The comment was about how good of a stat wins above replacement is.
So this afternoon I am trying to give Greg some piece of mind to how much stock can be put into WAR. I pulled the WAR Data for the Giants (I would have liked to do every team but I do have a day job and only an hour for lunch) and compared that to the Pythagorean Expected Wins and the actual wins for each team.
The Fangraphs data goes back to 2002 so this is the starting point and I looked at through last season (I didn't include this season because it isn't quite complete yet and I wouldn't want that to interfere with the results.) so a total of 8 seasons.
Here are the results:
Just looking at things with the naked eye suggests that they match up pretty closely. When you do a correlation you can see that both the Pythagorean and WAR predicted wins are highly correlated.
For a WAR even with the known issues a correlation of nearly 0.9 is very good especially when anything around 0.8 is considered to be strongly related. WAR can be improved especially in the measurement of defense and base running and even context specific results but even without these improvements it gives very robust results.
Fangraphs did a similar comparison looking at just last year's numbers and found very similar results of a correlation of 0.83. With that said I think that using WAR gives valuable information and I think that you can put a fair amount of stock into it.