Saturday, February 19, 2011

More WAR: Fangraphs vs. Baseball Reference. Roll Up, Place Your Bets, Fight! Fight!

Trevor Cahill 2010 = 4.1 Baseball Reference WAR
James Shields 2010 = -1.3 Baseball Reference WAR (that's minus 1.3 WAR)

That looks more like it (remember Fangraphs had them both at 2.2 WAR).

So why the big difference?

It's all to do with the difference in how the two sites calculate WAR.

Fangraphs uses FIP to calculate WAR - which is largely a predictive, rather than descriptive stat - so Fangraphs pitcher WAR reflects what a pitcher should've done - instead of being credited with what they actually did - this is the FIP formula - ((13*HR)+(3*(BB+HBP-IBB))-(2*K))/IP + constant* - theoretically removing luck - you'll see no mention to hits given up. In 2010 Trevor Cahill had a very low BABIP and gave up relatively few hits, (hence the low ERA) but struck no-one out - thus his FIP is rubbish, resulting in a low fangraphs WAR (and the K:BB ratio fans out there will be excited to see that K's and BB's are factored into FIP)

*the constant adjusts FIP to put it on a scale similar to ERA

In contrast, Baseball Reference WAR is calculated from the number of runs a pitcher allows As adjustments are made for whether he gives up more or less runs than the average pitcher playing in front of his defence, Baseball Reference WAR gives a pitcher credit for 'luck'/preventing hits/runs, and penalizes a pitcher for giving up hits/runs, and therefore is more descriptive than Fangraphs WAR. It also takes into account quality of opposition faced - whereas on Fangraphs, they tend to mock the idea that putting up good stats in the AL East vs AL West should weigh into Cy Young discussions.

There is a discussion on Fangraphs here, justifying their approach - both are valid, I guess, but it seems perverse to credit batters for luck, but penalize pitchers for luck when calculating what is supposed to be the same stat.

To be honest, if I were going to introduce a stat called 'Wins Above Replacement' and calculate it on a year-by-year basis, I'd credit a player for his actual performance that year, not what he should've done if he hadn't been lucky/unlucky. But as it is, both Fangraphs and Baseball Reference WAR can be useful. If you want to know what a pitcher actually contributed in a given year, use Baseball Reference WAR. If you want to know what they are likely to do this year (perhaps more fantasy relevant) use Fangraphs WAR - if FIP is useful for calculating future performance. We'll cover how to predict future performance in some exciting upcoming posts - with fancy graphs and original analysis.

And finally, the WAR-related video of the day is an '80s classic:

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