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Tuesday, October 21, 2008
FIP, extended
Jeff asked me to check out his blog. And this post is a response to that.
The run value of a GB is identical to the run value of the FB (if you exclude HR). More or less, here are the run values for all events, if you stick each PA into one of the groups below:
+1.40 HR
+0.33 HBP, Walk, Line Drive
-0.12 GB, FB
-0.30 K, Popup
(More or less. Just float the “-0.12” to whatever you need so that the overall sum at the league level is exactly 0.)
If you don’t want to separate the HR from the FB, and realizing that about 10% of FB are HR, then the run value of the FB is +.03 runs, and we get:
+0.33 HBP, Walk, Line Drive
+0.03 FB
-0.12 GB
-0.30 K, Popup
You can assume, if you like, that the line drive and popup rates are fairly random across all pitchers, and remove those from the equation, as are HBP. You now get:
+0.33 Walk
+0.03 FB
-0.12 GB
-0.30 K
Finally, the gap between GB and FB pitcher would be .15 runs, which is one-fourth the range of the walk and K range. Since we know that the K/BB ERA equation is:
5.4 - 12*(K-BB) / PA
, then all we need to do is make it the following:
?.? - 3*(4(K-BB)+(GB-FB)) / PA
And you simply set the ?.? to whatever you need to do match the league ERA.
I think that works, and maybe someone out there will verify it for me…
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