Anyway, for those interested, I created a SIERA Quick Calculator on Google Docs, of which anyone may save a copy. Follow the jump for Swartz and Seidman Cliff Notes:
According to our venerable authors:
SIERA accomplishes the following:
- Allows for the fact that a high ground-ball rate is more useful to pitchers who walk more batters, due to the potential that double plays wipe away runners.
- Allows for the fact that a low fly-ball rate (and therefore, a low HR rate) is less useful to pitchers who strike out a lot of batters (e.g. Johan Santana's FIP tends to be higher than his ERA because the former treats all HR the same, even though Santana’s skill set portends this bombs allowed will usually be solo shots).
- Allows for the fact that adding strikeouts is more useful when you don't strike out many guys to begin with, since more runners get stranded.
- Allows for the fact that adding ground balls is more useful when you already allow a lot of ground balls because there are frequently runners on first.
- Corrects for the fact that QERA used GB/BIP instead of GB/PA (e.g. Joel Pineiro is all contact, so increasing his ground-ball rate means more ground balls than if Oliver Perez had done it, given he's not a high contact guy).
- Corrects for the fact that FIP and xFIP use IP as a denominator which means that luck on balls in play changes one's FIP.
...And the formula:
SIERA = 6.262 – 18.055*(SO/PA) + 11.292*(BB/PA) – 1.721*((GB-FB-PU)/PA) +10.169*((SO/PA)^2) – 7.069*(((GB-FB-PU)/PA)^2) + 9.561*(SO/PA)*((GB-FB-PU)/PA) – 4.027*(BB/PA)*((GB-FB-PU)/PA)
From what I've ascertained with the Cubs, SIERA correlates pretty strongly with FIP and xFIP, tending about 0.5 to 0.2 lower -- but this just may be a FIP calibration difference. Anyway, it's pretty interesting.
Lastly: How should we pronounce this stat? I can't decide, so I'm adding a poll...