From: roger@crux.Princeton.EDU (Roger Lustig)
Subject: Re: Statheads and park effects
Originator: news@nimaster
Reply-To: roger@astro.princeton.edu (Roger Lustig)
Organization: Princeton University
Date: Sun, 20 Dec 1992 07:13:46 GMT

In article <28591@optima.cs.arizona.edu> dkl@cs.arizona.edu (David K. Lowenthal) writes:
>
>I have a question for the stat people.  How can you justify this
>park effect thing?  

By noting that the observations were made over a long period of time, and
showed substantial consistency.

>In other words, for every park prediction made
>on the net, how many are correct?  

Well, we make very few such predictions areound here to begin with.

Also, what do you count as "Correct"?  

>Doesn't is seem like stretching
>it a little to say that a player with a different team will play at the
>same level with his new team in a new park?  

That would be stretching it.  But nobody says that.  

Most predictions are based on the fact that players don't change radically 
from year to year for the most part.  That is, singles hitters rarely become
sluggers overnight, speedsters rarely become slowfooted in one season (to
say nothing of the reverse!), junkball pitchers don't develop a heater, 
and the ability to draw a walk tends to show early and stick around.

Now, if you were to make a prediction for a player, wouldn;t you start
with that player's record for the past couple years?  Wouldn't you then
consider age?  And wouldn't your best guess -- with some range for error --
be based on those things?

>Are players robots who you 
>can pick up and place in a new stadium and watch them do exactly the
>same things so that only the change in park matters?

Of course not.  Who has said that?  

But what can we predict about these "intangible" changes?  Nothing.
We can only go by the level of skill we've observed in the past, and
by our knowledge that players don't generally change radically from 
year to year.

>Before last season, several netters and I engaged in a "discussion" of
>how Greg Swindell would do with the Reds.  He came from a huge park,
>Cleveland, and went to a homer haven, Riverfront.  He posted an upper
>3's ERA with Cleveland the previous year.  I was scorned, especially
>by Valentine, when I suggested his stats might improve because he was
>playing for a better team, even though the park effect would suggest
>a downward trend.  Netters predicted a mid 4 ERA for him given the 
>park change and his tendency to give up homers.  He ended up with
>a mid to high 2's ERA.

Good for him!  Good for you, for guessing right.  Care to make 50 
guesses about 50 players who are changing teams?  We'll see how 
good you really are -- and how good everyone else is.  

(I mean it.  Let's get a pool together and predict performances for 
the free agents who changed venues.  COme up with a couple measures
of accuracy.)

>Obviously this is only one example.  But all i am asking is can you throw
>around park effects like they are gospel?  

Whom are you talking to?  Nobody around here does that.  Park effects
are very general things; but they do exist.  Almost everyone will hit more
homers in Wrigley or Atlanta than in the Astrodome.  THat doesn't mean
that Joe 'Stro won't fold upon being traded to the Cubs.  And nobody
around here has ever claimed otherwise.

>What percent of your predictions are correct?  

You've asked that twice now, and I get the feeling that you don't
know what these predictions represent.  

To answer the question: a lot.

>Players can adjust to new surroundings, and stat people
>don't consider that.  

Again, I'd like you to tell me who these "stat people" are, and how
you know what they don't consider.

>These kind of things are called "intangibles", or *luck* by Ms. Nichols.  

aSherri can defend herself, but I'd like to point out that she does 
*not* call adjustment "luck."  

On the other hand, can YOU predict how a player will adjust?  No, you
can't.  Did you predict Sheffield's big season?  Bonilla's utter inability
to hit at home?  McGwire's ultracomeback?  Boggs' fold?  

No.  You didn't.  Nobody did.  Nobody could without some inside info
that you and I don't have, and even with such info, it's unlikely that
 you could.  

We make our predictions based on the things we know to be reliable
in most cases.  We don't throw up our hands and say "you can;t predict 
anything, because all kinds of things could happen."  That's because 
we don't use an impossible definition of "predict."

>For example, can't a pitcher who just pipes
>the ball because he pitches in the Astrodome start nibbling the corners
>when he gets traded to Riverfront?  

Sure he can.  Does it happen often?  Did that pitcher do this on his 
two or so annual starts in Cincy?  Besides, if he *has* that control,
won't he do better in Houston, too?  

>Can't a hitter who hits 20 homers
>in Oakland take one look at the short Yankee porch and hit fewer homers
>because he wants to pull everything (cf. Dave Revering)?

Again, sure.  What's your point?  Are you telling me that you CAN look
inside a player's brain and see how he's going to change his game?
You can't.  You can only go by what you know of past performance.  You
don't know whether his girlfriend will die, or he'll get allergies, or
his son will win the Spelling Bee, or whatever.  You can only go by 
the same things that everyone else goes by: past performance.  

>Just Curious,

Yeah.

Roger