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September 22, 2011

Between The Numbers

Addition by Addition

by Colin Wyers

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I’m going to introduce a few new stats for our sortable reports and cards in just a moment, but first I’d like to talk about what kinds of things we’re looking to add and what our decision process looks like.

Our readers really like baseball stats, but they like looking at ones that matter. It’s our job to make sure that our statistics matter, that they communicate something meaningful, and that they do it in a useful way.

For us to add a stat, it doesn’t have to be world-shaking. It can merely be interesting (and some people may not even agree on that). But it does have to meet a few criteria:

  • It needs to be different enough from our existing metrics to provide added value. Perhaps not substantivelyit can say the same thing, so long as the presentation is different enough that there’s some value in having both presentations.
  • When a new metric disagrees with an existing metric, it’s important to make sure that we can clearly communicate why the two differ, and what the value is to having both answers. If we think one metric is provably better than the other, we use that one instead.

We plan to continue adding things to our sortable reports over the offseason, but when we do so it’ll be guided by those two considerations. Now, on to the fun stuff.

We’ve introduced two new metrics that should seem rather familiar to most of you, even if we’ve never presented them ourselves. They’re “plus” metrics, similar to OPS+ and ERA+ from Baseball Reference.

Let’s start with RPA+ (RPA_PLUS in the sortables), which is our new offensive rate stat along the lines of OPS+. What it isn’t is a departure from how we evaluate hitters currently; TAv and RPA+ will return the exact same rank order of batters. At the core of both of them is the exact same adjusted runs per plate appearance, figured using linear weights values derived from run expectancy tables. In this case, there is no right or wrong way to handle the scaling of adjusted R/PA for presentationsome people find it more intuitive to look at R/PA scaled to batting average, others to 100. (There are also technical reasons to prefer either, based upon what you’re doing with each.) Essentially, they’re two ways of looking at the same informationcomplementary, rather than redundant or competing.

So why might you prefer RPA+ to OPS+? There are a few reasons:

  • RPA+ includes a league quality adjustment. Batters in the AL face tougher pitchers, and so the same batting line in the AL means a better hitter. TAv and RPA+ capture this, while OPS+ ignores it.
  • RPA+ is a better estimate of a batter’s production than OPS+, which undervalues high OBP, low SLG players and overvalues high SLG, low OBP players.

The complement to RPA+ is Fair RA+, again similar to ERA+. Unlike with RPA+, Fair RA+ will return a different order than Fair RA, because it includes park and league adjustments. Why favor Fair RA+ over ERA?

  • Fair RA separates what a pitcher has done from our estimate of his defensive support.
  • Fair RA uses all runs, not just earned runsERA+ will overrate a groundball pitcher relative to a flyball pitcher with equivalent production.
  • Fair RA uses a different construction to produce the scaling factor. ERA+ is actually the league average ERA divided by the player’s own ERA, in order to make larger values better (rather than allowing smaller values to be better). We take Fair RA, divide by the league average, and subtract the result from two. This gives the same “bigger is better” property ERA+ has but keeps the units meaningful and makes it easier to work with mathematically. Patriot explains the reasons for this, but in summary, taking a weighted average of ERA+ across seasons is more unnecessarily complicated, and it makes the units of ERA+ essentially meaningless. A Fair RA+ of 110, for instance, means a pitcher's Fair RA is 10% better (that is to say, lower) than the league average. ERA+ doesn't behave linearly at all. Comparing the two methods, setting 4.5 as the league average:

    Graph of the two methods of normalizing to league average.

What I've called "two-minus" is the method we are using; "inverse" is the method behind ERA+. What you find is that an additional 10 points of ERA+ means different things based upon where on the curve that additional 10 points occurs, while 10 points of Fair RA+ consistently means the same thing for any point of the scale.

Since I’ve taken the time to point out yet again how OPS falls short of linear weights-based measures of offense, I’d also like to announce that we’ve included TAv and RPA+ on the batter and pitcher opponent quality reports. We’ve retained the slash lines and OPS as well, but this is one place where we can put our money where our mouth is as far as putting our preferred offensive metrics out there for consumption. We’ve also added TAv against for pitchers, for those who want to see a pitcher’s performance in those terms. (Yes, TAv against attributes all fielding performance to the pitcher. Under consideration is a derivation of TAv against that is more DIPSy.)

We’re also introducing a new breakdown for batting WARP, which you can find in this custom sortable report. We’ve broken WARP apart so you have a better idea of what goes into each players’s numbers. Included are:

  • Batting Runs Above Average, or BRAA
  • REP_LEVEL, which is the amount added to a player’s BRAA to give us runs above replacement.
  • POS_ADJ, which tells you how many runs a player is credited based on his fielding position,
  • And TOT_DEF, which is POS_ADJ plus a player’s FRAAin other words, everything in WARP that measures a player’s defensive abilities.

This is only the startwe’ve got some other things cooking, and we’re really excited to continue to improve these sorts of offerings. (Of particular interest is defense for catchers, including Mike Fast's work on catcher framing.)

And as a reminder, while the default sortables are available to everyone, custom sortables are reserved to subscribers only. Right now, you can save six bucks on a yearly subscription with our Big September coupon code.

Colin Wyers is an author of Baseball Prospectus. 
Click here to see Colin's other articles. You can contact Colin by clicking here

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23 comments have been left for this article. (Click to hide comments)

BP Comment Quick Links

Mooser

Fantastic, particularly the WARP breakdown. Colin, can you tell me if the new FRAA includes ratings for OF arms and / or infielder DPs. If not, will that be an enhancement down the line?

Sep 22, 2011 05:52 AM
rating: 2
 
Mooser

Sorry one more question. Positional Adjustments for pitchers are higher than any other position. Thus, when added to the FRAA in Total DEF, it pushes all the pitchers to the top of this list. Is this the right way to present this, as I didnt think that BP positional adjustments were based on fielding difficulty as much as average hitting ability of the position.

Sep 22, 2011 05:58 AM
rating: 0
 
CRP13

I applaud the effort to bring the "baseball stat" community together by adopting usage of stats found elsewhere that you agree with. I think it's a good step in making advanced statistics in baseball more widely-accepted by normal people.

Sep 22, 2011 06:20 AM
rating: 4
 
jrmayne

Could you expand on your statement that OPS+ undervalues OBP? OPS+ values OBP at about 1.25 slugging this year. What's the approximate ratio that your stat uses?

Thanks.

Sep 22, 2011 08:17 AM
rating: 0
 
BP staff member Colin Wyers
BP staff

It's going to vary based on the composition of the OBP and the SLG - a high-walk OBP is different than an OBP coming from a high batting average. In general, though, it's going to be about 1.8:1 for OBP versus slugging. I've seen some analysts say stuff like 1.74 or the like - like I said, it depends a bit on a number of factors, which is why we don't just simply use OBP and SLG to come up with TAv or RPA+. But it at least gives you a sense of how linear weights based stats of all stripes value OBP relative to OPS+, or even to OPS itself, which underweights OBP even more than OPS+.

Sep 22, 2011 08:32 AM
 
jrmayne

Thanks. This is very helpful.

Sep 22, 2011 09:54 AM
rating: 0
 
jhardman

You are Baseball Prospectus. Offer up every sortable stat under the sun. At least three times more than you can get anywhere else and even make up a few that stump your stat base.

I want to see pitcher stolen bases and pitcher stolen base percentage. I'm talking about pitchers as offensive players. Heck, throw in pitcher home runs as well. Break down each pitcher's offensive stats. (I know a lot of this is available already.)

The more, the merrier.

Sep 22, 2011 09:15 AM
rating: 1
 
BP staff member Dave Pease
BP staff
(2)

If we don't think a stat expresses anything useful we're not going to go out of our way to include it.

Sep 22, 2011 14:01 PM
 
Richard Bergstrom

Hey, Mitch Williams hitting a grand slam had value.. and was darn funny to watch.

Sep 22, 2011 19:51 PM
rating: 0
 
ncooke

"Batters in the AL face tougher pitchers"

Is this true? I guess it may be, but I'd never thought of it this way. I'd always thought the AL/NL difference was that pitchers faced 12.5% more "real" batters due to the DH, plus the AL East spending machines consolidates some quality there overall, making winning harder for the rest of the AL. But in focusing just on pitchers, I'd have guessed that the Phillies, Braves, and Giants match up pretty well with any three in the AL, and the rest of the pack in either league doesn't strike me as that imbalanced.

Just caught my eye and made me wonder...

Thanks for all this, though.

Sep 22, 2011 12:52 PM
rating: 1
 
BP staff member Colin Wyers
BP staff

What we do is we look at how individual batters perform when they play against pitchers from each league (so team switchers and interleague play). Even after adjusting for park, the same hitter will hit better against NL pitchers (in the aggregate) than against AL pitchers. We're comparing each player to himself, so this is unrelated to the DH. We're also adjusting for quality of opposing pitcher relative to league, so if a guy faces a disproportionate amount of good or bad pitchers during interleague it's not going to throw the results off.

Playing baseball in the American League is harder than playing baseball in the National League, something we get reminded about every time interleague play rolls around and then we promptly forget about, because for the vast majority of the schedule the AL plays the AL and so nobody really notices the disparity. But it's real, it's not just a consequence of the DH and it shows up in the stats of individual hitters and pitchers.

Sep 22, 2011 14:40 PM
 
John Carter

Nice.

1. Colin, please, help me understand how does OPS+ not include a league adjustment? Isn't it based on the league average?

2. You don't mention a park adjustment in RPA+ (or I missed it). Does it have it? (If it does not, then FRA+ is not a precise compliment.)

3. How does ERA+ overrate a groundball pitcher relative to a fly ball pitcher?

4. I can see ERA+ overrating pitchers with a good defense or good relievers to back him up. Does FRA+ get around those issues? Assuming not, are we getting a defense independent measuring stick in the + format?

Sep 22, 2011 15:00 PM
rating: -1
 
John Carter

Oh, sorry, I didn't see the post just ahead of me (I guess I needed to refresh before clicking on the "Show comments" line that had been up all afternoon). That answers question no. 1.

Sep 22, 2011 15:06 PM
rating: -1
 
Pat Folz

Not Colin, but:
3)I believe it's because errors are more likely on groundballs than fly balls, so GB pitchers get a little "boost" to their Earned RA relative to FB pitchers.

4)From the article: "Fair RA separates what a pitcher has done from our estimate of his defensive support."

Sep 22, 2011 21:00 PM
rating: 0
 
BP staff member Colin Wyers
BP staff

TAv has always been park-adjusted, and so is RPA+ - I didn't break it out explicitly as it doesn't differentiate from OPS+, which is also park adjusted.

As for ERA+ and groundball pitchers - an error is more likely to occur on a groundball than a flyball. So if you take two pitchers of otherwise equal production (measured by RA), the groundball pitcher will tend to have more errors behind him and thus more unearned runs.

And yes, Fair RA both accounts for defensive support and inherited/bequeathed runners, and so Fair RA+ accounts for them as well.

Sep 22, 2011 21:25 PM
 
FlyByKnite

Ya know, maybe I'm blind here but I don't see it in the sorted stats section. Can someone help me? Perhaps lead me by the hand.

Sep 22, 2011 18:19 PM
rating: 0
 
BP staff member Colin Wyers
BP staff

RPA+ isn't currently in the default reports, but you can include it in a custom report (it's listed as RPA_PLUS in the selection list.)

Sep 22, 2011 21:26 PM
 
FlyByKnite

Thank you sir.

Sep 22, 2011 21:59 PM
rating: 0
 
Richard Bergstrom

Regarding criteria: An important factor to me is that the metric agrees with itself and people agree on how the metric should be used. It has to have internal consistency, so to speak. That's one of my beefs with FRAA where it seems the numbers on a certain player vary wildly from year to year and even in the BP Annual, will contradict what is in that player's comment section.

On another note, I'm not quite clear how TAv and RPA+ are different besides one being formatted/evaluated like batting average and the other formatted with 100 as a baseline for league average. Does that really make RPA+ a new metric? That'd be like saying a .300 hitter gets a base hit 30% of the time and calling that 30% a new metric.

Sep 22, 2011 19:56 PM
rating: 2
 
TangoTiger

It's the same metric, set to a different scale, if you want to get technical.

***

For Fangraphs readers, it's akin to wRC+ on their site. All the metrics at Fangraphs and now at BPro courtesy of Colin, have as their basis Linear Weights (long live Pete Palmer). They differ basically in their park adjustments.

You see that at the very top with Bautista at 181 at Fangraphs and 199 at BPro. Otherwise, the two lists are reasonably similar.

Sep 22, 2011 22:52 PM
rating: 0
 
joepeta

Colin, Regarding more future changes: Is WXRL coming back? It disappeared from the sortable statistics at the beginning of the season with no explanation?

Sep 26, 2011 06:00 AM
rating: 1
 
Adrian

Nice additions - is there any chance we can get more of these advanced statistics incorporated into the Pecota cards? I like the predictive aspects of Pecota, but I really miss the wealth of information that was broken down and presented on the old DT pages. It's a small gripe but it would be nice to have.

Also, any idea when advanced stats will be available for pre-60's players again? Again it's a small thing and I'm sure it's being worked on, but it would be cool to have again.

Anyway, thanks for the recent updates and additions, and keep up the great work.

Sep 29, 2011 09:43 AM
rating: 1
 
Rob Miller
(162)

It would be SUPER helpful if you would provide Player_id as a downloadable field. I ask. I hope. I have yet to see.

Oct 12, 2011 13:09 PM
rating: 0
 
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