From: mjones@fenway.aix.kingston.ibm.com (Mike Jones)
Subject: Re: defensive measures of performance (was -- Re: Lists: The Best Players In Baseeball)
Date: Fri, 08 Jan 93 23:36:32 GMT
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cmk@athena.mit.edu (Charles M Kozierok) writes:
: In article <steph.726521280@pegasus.cs.uiuc.edu> steph@pegasus.cs.uiuc.edu (Dale Stephenson) writes:
: >In <1993Jan8.032738.23621@athena.mit.edu> cmk@athena.mit.edu (Charles M Kozierok) writes:
: >>based on your comments, and the post by Clay where he explains
: >>what the DA and RF are (thanks, btw), i would have to conclude that
: >>these statistics definitely are bogus. i don't know why anyone would
: >>use them to judge much of anything. i know i wouldn't.
: >Why use it?  Because, (lousy as it is) it's the best I have available to me.
: (oh boy, i can just *see* Roger Maynard drooling over this one... :^)
: all i will say is that a lousy statistic is *worse* than no statistic at all.
: i believe that should be self-evident.

Not always. It depends on how lousy. There are statistics that don't give
you all the information you could get (like batting average), and those that
are downright misleading (like RBI totals for individual hitting
performance). Those in the second category are definitely worse; those in
the first category are often progress toward something better. I believe
that Dale was talking primarily about range factor witht the "lousy as it
is" comment; RF is significantly flawed compared to DA. On the other hand,
with a suitable knowledge of what its biases are, it can be useful (again,
like RBI totals).

: >So why use it all?  My alternatives would be 1) Error Totals, which is worse
: >than range, and 2) Gold glove voting. Given who does the voting, I find it
: >hard to believe that it correlates better with reality than range factors.
: >In individual cases (Alomar?) it might, but as a general rule?
: you sound like a smart guy. invent something better! start with one
: of the stupidistics and make the necessary adjustments. or start with
: a clean slate.

The problem is that the evidence for a better measure is not readily
available (talking about RF). If all you have is PO, A, and E then range
factor is about the best measure you can construct from it. It's very much
the same case as if the only commonly available offensive statistics were
H, AB, and HR. What could you do with that? You could calculate batting
average and make a crude guess at SLG, but it wouldn't be exact. Would it be
better than nothing? Sure thing. DA is a whole 'nother kettle of fish,
though.
  
: >And defense *is* important, and should be talked about.  So I can't leave it
: >alone.
: then i think we should at least attach a good-sized list of caveats to
: any evaluation that uses those stats.

For RF? Certainly. For DA? Unclear.

: >Range does have the advantage of measuring something positive the
: >player did do -- make outs.  If Alomar gets less groundballs than any other
: >AL second baseman, despite making *every play* hit his way, is his stellar
: >defense really that valuable to the Jays?
: that is actually an interesting point.

In fact. Many of the anti/stathead arguments that go on here are because of
misunderstandings about the difference between raw value of a player and
value of a player in context. Alomar probably isn't worth as much to the
Jays as he would be to a team with a massive groundball staff, but he's
still a *very* good player.
  
: >>maybe subjective judgment actually wins out here. or maybe someone
: >>can come up with a new stat that actually makes some sense.
: >Defensive Average makes sense to me.  It's going in the next revision of my
: >baseball game.
: what about park effects? how can it be of any value without park effects?
: surely you could do better than the current definition.

OK, time for the brief DA explanation. The field is divided into zones. The
zones, taken together, cover the field (fair and fould ground). Every batted
ball is observed and classified as ground ball/fly ball (subjective, but not
difficult), and its location (zone) is recorded. I believe the folks who
collect this have several people scoring each game to minimize bad
locations. A player's DA is just the percentage of balls hit into (through)
his zone that he converts into outs. If a player makes a play outside his
zone (say a 2B going behind second into the SS's zone), two things happen:
the player who made the play gets credit for an out, and the player whose
zone the ball was hit into gets charged with an "opportunity". Typically we
look at groundball DA for infielders and flyball DA for outfielders. The
stat hasn't been around long enough to have been excruciatingly analyzed,
but it does seem to show some good characteristics:
  - DA for a given player doesn't fluctuate widely year-to-year, in general
  - DA doesn't change massively when a player changes team
These indicate that there probably isn't a massive "park effect" problem, at
least for infielders and most outfielders - I'd be surprised if the
outfield shapes in the extreme cases (like Fenway) don't affect the
fielders' DA, and that DA is actually measuring a characteristic primarily
of the player, not the park or pitching staff. Since we normalize for
opportunities, DA eliminates the primary problem of RF (the Alomar effect,
as it were). DA probably isn't perfect, but it looks pretty good to me.
  
: >Note that Defensive Average does not suffer from the distribution problem,
: >and therefore is much more reliable than range factor.  It still may suffer
: >from park effects, and of course distribution of "hard" chances, but I'm
: >inclined to believe those effects would be minor.
: really? how can playing on turf versus playing in the "heavy rough" in Detroit
: not have a significant effect on ground balls? i find that *very* hard to
: believe.

It probably does have an effect. The question is whether the effect is
something we should worry about. We don't adjust batting averages for grass,
turf, big green walls in left field or ivy. Why, for a basic measure, whould
we want to adjust the defensive equivalent for park? If I had home/road DA
splits lying around, it would be easy to develop defensive "park factors",
but the evidence (admittedly from small sample size) from players who have
changed teams implies that, especially for infielders, the effect is
generally small.

: >I definitely have more faith in it than in subjective judgement.
: well i understand not wanting to use a subjective judgment. but DA sounds
: pretty bad, even if better than RF. your decision to use DA instead of
: subjective judgment sounds primarily like a... well... subjective judgment.

Given the explanations that I've presented above about DA, I'd really like
to hear what you think is wrong with it. I think it's pretty good, but if
I'm fooling myself I want to know about it.

   Mike Jones  |  AIX/ESA Development  |  mjones@donald.aix.kingston.ibm.com

He's got a gun concealed about his person. They can't tell me he throws them
balls with his arm.
	- Ring Lardner, on Walter Johnson