xERA Formula

[tag0519]

Hi All,

I'm trying to find the formula for xERA. My apologies if I missed it on the site. I know there are some season-specific constants and a normalization factor in the the formula. Where can I find those constants and normalization factors?

Thanks in advance,
-Tom

[RAY@HQ]

Yes, our Glossary is well-hidden, the formula is in there though. I've asked Ron to provide the normalization factors, as I don't have them handy.

[tag0519]

Thanks !!

[RON@HQ]

We don't use the Gil and Reeve version anymore, except for minor league data that appears in the Forecaster (because we do not have access to accurate FB and GB data for minors). The Burnson model is what we use now and does not require a normalizing factor:

Expected earned run average2 (John Burnson)
xER = xER%*(FB/10) + (1-xS%)*[(0.3*BIP-(FB/10))+BB]
where
xER% = 0.96 - 0.0284*G/F
xS% = 64.5 + (K/9*1.2) - (BB/9*(BB/9+1))/20 + (0.0012*GB%^2 - 0.001*GB% - 2.4)

[tag0519]

Cool... Thanks Ron

[tag0519]

one more qq - Whats FB and BIP?

[RAY@HQ]

Fly balls and balls in play.