How do you calculate WAR for RP?

by nny on Aug 1, 2009 1:18 PM EDT

I figured this would probably be the best place to ask.

The only place I've found online that even gets into is fangraphs. However, they very rarely ever actually gave formulas, it's mostly just words, which is very annoying. Would be so much easier and efficient if they just posted the formula then explained the variables.

But I digress.

At -> http://www.fangraphs.com/blogs/index.php/pitcher-win-values-explained-part-seven

He does give the basic formula for SP, which is (((18-AIP) * LRPG + AIP * FIP)/18)+2)*1.5

Where

AIP=Average IP per start

LRPG=Leage's average Run Per Game

and FIP=Fielding Independent Pitching.

This is the part that should be different for RP. Afterall, you can't have an average IP per start for RP lol. But what's the formula for this part for RP? The rest should all be the same, outside of the league average win percent added for RP, but that's addressed in an earlier posted (.470%).

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Formula:

X is (RS+RA)^.267, which should be some number similar a tenth or two below 2.0
RS is league-average runs scored per nine innings (not just earned runs).
RA is the reliever’s runs scored per nine innings (not just earned runs).
.470 is the rep level winning percentage for relievers. It’s more like .460 for AL relievers and .480 for NL relievers.
IP is easy.
The (LI + 1)/2 part is a shortcut that takes into account the leverage of the situations a pitcher pitched in, plus bullpen chaining. Bullpen chaining basically accounts for the fact that a if a closer is injured, he won’t be replaced by a scrub. Instead, the scrub goes at the end of the bullpen and everyone is bumped up a notch and the setup guy is the new closer. For more, read this: http://www.beyondtheboxscore.com/2009/4/29/856308/bullpen-chaining-and-reliever-war

I don’t think that’s how Fangraphs does it, but that’s how I’d do it and the results are probably pretty similar. For RA, you probably want to use tRA, FIP/.92 or something else that accounts for fielding and park.

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by Sky Kalkman on Aug 1, 2009 4:57 PM EDT reply actions

Oops, exponent of (RS + RA) is .287, not .267.

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by Sky Kalkman on Aug 1, 2009 4:58 PM EDT up reply actions

And crap, formula got deleted by autoformat. Grrr.

{ [ RS^X / (RS^X + RA^X) ] - .470 } * IP/9 * (1+LI)/2

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by Sky Kalkman on Aug 1, 2009 4:59 PM EDT up reply actions

yeah using tra

thanks a bunch. I’d kiss you if that’s your kinda thing.

by nny on Aug 1, 2009 5:37 PM EDT up reply actions

Either way, I appreciate the sentiment.

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by Sky Kalkman on Aug 1, 2009 8:59 PM EDT up reply actions

What's FIP/.92?

Other than the obvious math. Never heard of this.

Marlin Maniac, a Florida Marlins blog

by SFiercex4 on Aug 1, 2009 11:31 PM EDT up reply actions

RA * .92 = ERA, roughly

Or, 92% of runs are earned.

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by Jack Moore on Aug 2, 2009 12:22 AM EDT up reply actions

Yup, it puts FIP on the RA scale instead of the ERA scale.

Not perfect, but should be fine for most uses.

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by Sky Kalkman on Aug 2, 2009 7:55 AM EDT up reply actions

since you're so helpful :D

We’re projecting future WARs, is it better to use the regressed tRA (aka tRA*) or normal tRA?

I’d assume normal tRA (and hoping because I’ve never worked with regression before lol), but better to ask more knowledgeable people :D

by nny on Aug 2, 2009 8:27 PM EDT up reply actions

err spelling

When projecting*

by nny on Aug 2, 2009 8:27 PM EDT up reply actions

At least tRA*.

More preferably you’re using three years of data. (Especially for relievers, who get such small sample sizes even in a full season; the most you’re likely to get out of a short reliever is, what, 80 IP?)

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by cwyers on Aug 2, 2009 10:47 PM EDT up reply actions

projecting minor leaguers

so depends what league they’re in. doing both SP and RP.

Would I regress to the league numbers, project the ML numbers based off the regression, then regress those to the MLB numbers?

Only regress MILB numbers? Only the MLB numbers?

by nny on Aug 3, 2009 11:40 AM EDT up reply actions

You'd need to translate the minor league numbers.

Which is tricky – ideally you’d translate the individual components and then do the component ERA (which is what tRA is). MLEs are hard, very hard, to do right.

As far as what to regress to – it’s a tough question. That’s actually the subject of my THT article for this week, and the answer is not as clear-cut as I think you’d like.

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by cwyers on Aug 3, 2009 11:52 AM EDT up reply actions

You can never go wrong with regressing to the mean

F*** Billy Beane... actually, I kinda like Holliday

by vivaelpujols on Aug 5, 2009 2:47 AM EDT up reply actions

Sure you can!

You can do anything wrong.

Here’s what it comes down to – which mean are you regressing to?

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by cwyers on Aug 5, 2009 11:03 AM EDT up reply actions

I would say the league mean

But I guess you think you should regress to the population mean. However, it’s hard to know, except in obvious cases, which population a player falls into. That’s why in most cases, it’s seems okay to regress to the league mean.

F*** Billy Beane... actually, I kinda like Holliday

by vivaelpujols on Aug 5, 2009 3:12 PM EDT up reply actions

Which league, though?

We’re talking about projecting a minor leaguer as a major leaguer – so do you regress them to the league mean for the league they are currently in or the league you’re projecting them to?

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by cwyers on Aug 5, 2009 7:52 PM EDT up reply actions

Well it depends on how many plate appearances they rack up

There is obviously no cutoff, but after say, 600 plate appearances, you could say that this guy is a “major leaguer” and you would regress to the major league mean.

F*** Billy Beane... actually, I kinda like Holliday

by vivaelpujols on Aug 5, 2009 8:00 PM EDT up reply actions