Comparing Pitchers

The Fourth Outfielder has a great post on comparing pitchers. As Meagher looks at the folly of comparing two Giants pitchers who were mentioned in the same breath in a Dodger Thoughts thread, he makes this observation:

This speaks to what I consider to be perhaps Bill James’ greatest insight. Baseball is full of numbers, he argued, but the typical application of numbers in baseball was based not on the contextual meaning of those numbers but on the emotional and associational impact of the numbers. .304 average? Sign me up! 31 home runs? Wow, a big bopper! James argued that his goal was to strip away that veneer and determine which numbers were important and why.

And later:

In terms of predictive value, the number of innings a pitcher throws in one season doesn’t heavily influence the number he’ll throw in future seasons. There will be correlation, of course, because pitchers are used in fashions that reflect their skill set and because some pitchers have recurring injury issues. However, those are reflected in other statistics as well, and IP doesn’t tell you anything substantial about a player’s true talent level that couldn’t be unearthed with other metrics.

Similarly, ERA doesn’t have great predictive value. A player’s ERA’s will often end up being similar in many years, but it’s the components of ERA that matter in determining how effective a pitcher is. To project pitching performance, it’s necessary to look at how often a pitcher strikes batters out, walks batters, and so forth; it’s not necessary to look at the player’s ERA.

The so forth would include home run rates and park factors. These, with the things Meagher mentions, are the peripheral numbers I referred to in the comments on a previous post.