Tuesday, September 27, 2011

Pitching Winning Percentage and fWAR

I have been super busy with work and life in general and have neglected writing far too much. This afternoon I had the time to have a little fun with excel and the wealth of data that is Fangraphs.

I have always been curious how much winning percentage is associated with fWAR and decided that now would be a good time to take a look. I pulled the data from the last 3 years for pitching seasons with at least 100 innings thrown. I then plotted the data and took a look at the correlation.

So I proudly present the correlation between fWAR for pitchers and Winning Percentage:

As you can see from the scatter plot there is some positive correlation between winning percentage and fWAR but it isn't super strong. Excel told me that the correlation to about 0.49 which makes sense.

A high winning percentage usually means that a pitcher did well as does a low winning percentage usually means that a pitcher did poorly but this is not always the case and in the data set that I have here it seems that high winning percentage is more often than not a a false signal for a good pitcher.

Here are all the pitchers who had a winning percentage of 0.6 or greater with at least 100 innings pitched:

We essentially see the whole gambit of pitcher quality here from MVP caliber seasons to a season of below replacement level performance with almost no observable trend that a higher winning percentage leads to a higher fWAR.

So in the end this was a fun little experiment. We found that there is a relationship between winning percentage and fWAR which makes sense but that it really doesn't tell us more than what we already knew, that good pitchers will tend to have higher winning percentages but that doesn't mean people with low winning percentages are bad or that pitchers with high winning percentages are good.

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