From: genetic+@pitt.edu (Dr. Dave)
Newsgroups: rec.sport.baseball
Subject: Re: Statheads and park effects
Date: 21 Dec 92 03:56:10 GMT
Organization: Department of Industrial Engineering

Thus spake dkl@cs.arizona.edu (David K. Lowenthal):
>
>I have a question for the stat people.  How can you justify this
>park effect thing?  

It depends on which "park effect thing" you are talking about.  There are
at least 2 different park-related adjustments that people try to make.  They
have different justifications, and not everybody subscribes to both/all of
them.

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

OK, since you're talking about "prediction", you must be referring to what
I'll call "Predictive" park adjustments.  These are attempts to estimate how
a given player's batting or pitching stats would be affected were he to move
to a particular new home park.  You should be aware that most people here,
when they talk about "park adjustments", are *not* talking about Predictive
park adjustments (unless, of course, they say so specifically).

Predictive park adjustments are fuzzy guesswork, based on looking at what a
given park does to the league as a whole, and on the player in question's 
road batting stats and batting stats at the park he's moving to.  Then come
the fudge factors, in which it is noted that "he's a line-drive hitter", or
whatever.  Personally, I try to avoid this sort of thing, although it is of
course fun to speculate.

>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?  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?

No.  On the other hand, when most of us talk about park effects, we're 
talking about *retrospective* park adjustments to players' raw batting stats,
as a way of adjusting for that fact that runs are not of equal value in all
parks.  In parks where runs are (relatively) easy to score, like Wrigley
Field and Atlanta/Fulton Co. Stadium, individual player offense needs to be
deflated in recognition that it's easier for the *opponents* to score runs
there, too, and thus you need to score *more* in order to win than you would
need to score in, say, Oakland or Houston.

>Obviously this is only one example.  But all i am asking is can you throw
>around park effects like they are gospel?  What percent of your predictions
>are correct?  Players can adjust to new surroundings, and stat people
>don't consider that.  These kind of things are called "intangibles", 

They're called intangibles because they are intangible: you can't see them,
or their absence.  Which makes them useless for prediction, for you as well
as for us.  If Swindell pitched better for "intangible" reasons, then we'll
never know that.  Maybe it was mechanics.  Maybe it was a particular affinity
for the mound at Riverfront.  Whatever it was, the park-adjusted guess at
his ERA in Riverfront was still the best guess available.

(Personally, I *never* attempt to predict performance in a player's first 
year in a new league.  There are just too many variables.  If Swindell reverts
to that 4+ ERA this season, will we say that the hitters are used to him, and
he's reverted to his true level in that park, or will we say that he's lost
his chemistry/attitude/intangibles?)


-- 
       David Tate        |"Out of the dugout endlessly swinging,
 dtate@unix.cis.pitt.edu | Out of the manager's throat, the sound fundamentals,
 Prof. of Story Problems | Out of the six-month season..."            
 Member ORSA, TIMS, SABR | 	Walt "Lefty" Whitman
Newsgroups: rec.sport.baseball