I love hearing that Colin is getting involved and have a lot of faith in his testing. I'm excited to see his results. Again, a great add to BP and I expect PECOTA will be just fine with his help.
I think of .92 as a league wide average. In reality the conversion rate will change depending on a team's defense but if we are just trying to consider the pitcher's talent we want an average defense. We use .92 to go from ERA to RA when tRA or FIP gives us a pitcher's talent (independent of defense) in ERA and we want it in RA.
Great article and it's always nice to hear more about the concrete impact of Moneyball.
Would there be use in a DIPS system like tRA that does not include line drives? Is this what David Gassko created with his Luck Independent Pitching Statistic? Any thoughts on that metric?
I also don't know the code for tRA* but I suspect they would regress LD heavily toward league average. I know they do other regressions to but perhaps this is a way to improve a DIPS metric.
I can see why FIP is scaled to ERA, because it imagines all pitchers have the same batted ball profile. And says HRa is a skill. I see xFIP as reclassifying that HRa skill.
Anyway, this is why I think using one number (.92 or whatever) to go from ERA to RA is fine. When we start looking at a pitcher's GB profile should we start to incorporate a changing ERA to RA factor? How different is the ERA to RA conversion for extreme fly ball pitchers and extreme ground ball pitchers? Isn't this a reason to check against RA?
But perhaps a test against RA would include a teams defense. Does GB profile effect ERA to RA difference? Thoughts?
No, it's a skill based indication of a pitcher's talent (at creating ERA) in 2009. This is going to be a better indicator of 2010 ERA than 2009 ERA. A prediction of 2010 ERA is something along the lines of PECOTA. I imagine SIERA informs PECOTA a lot.
I meant to write xFIP not FIP so I'd be looking for those same charts but with the corrected xFIP. Also is there any hope of adding tRA* to the testing?
Thanks for the update. I don't mind the errors so long as they are handled in this transparent and respectful manner. I think this says a lot for the great "peer review" within the sabr community. (As well as existing work.) Keep up the good work and I'm excited to see how SIERA can be improved. In the mean time I'd love to see a SIERA vs FIP comparison for specific types of pitchers. Considering the great quality of work thus far, I expect that will be up within the week.
Hey thanks for SIERA, I'm loving the new BP. I expect a few tweaks and an approval from Tango shortly. But I have a few questions
If I want to look at future ERA I would use TRA* instead of TRA as they advise on StatCorner. How does SIERA do against TRA* for predicting next year ERA?
I also understand if you don't want to include any metric that regress the components. But what about a SIERA*? Would this be better than SIERA at predicting next year ERA? And what about when SIERA* means an individual regression rather than regressing toward league average. So how does SIERA do at predicting 2009 ERA when you input a Marcel produced from 2006-2008 data instead of just 2008 data?
I've met Wagner several times and he is a complete class act. I'd love to hear him talk about his relationship with Sandy Koufax as I know they've been in contact since Wagner was with the Astros.
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