From: gindin@gindinraleigh.ibm.com (Jim Gindin)
Subject: Re: NL OPI Final
Date: Wed, 07 Oct 1992 19:59:54 GMT
Reply-To: gindin@gindinraleigh.ibm.com (Jim Gindin)
Organization: ELC

In article <1av7nlINNn8s@usenet.INS.CWRU.Edu>, sfh@po.CWRU.Edu (Steven
F. Hubbard) writes: 
> 
> In a previous article, schmke@cco.caltech.edu (Kevin Todd Schmidt) says:
> 
> >      0.74*1B + 1.28*2B + 1.64*3B + 2.25*HR + 0.53*BB + 0.34*(SB-2*CS)
> >OPI = ----------------------------------------------------------------
> >                              AB - H
> >
> >BA = H / AB
> >
> >SLG = (H + 2B + 2*3B + 3*HR) / AB
> >
> >OBA = (H + BB) / (AB + BB)
> >
> 
>   What is OPI designed to measure?  It looks like something per out, but what
> is that something?  I understand BA, SLG, and OBP, but the OPI formula is
> rather cryptic.
> 
>   Along the same lines, what does OPS measure?  It combines two numbers that
> I understand into some master quantity.  Having read this group off and on
> for about 2 years, I've learned to rank players' offensive production by
> OPS.  Does it measure a specific skill besides the rather vague sounding
> "skill at batting"?

My interpretation of this formula is that it is an attempt to measure a
player's
contribution to runs scored by his team in relation to the outs
(oppotunities) he
costs his team.

The coefficients in front of singles, doubles,... walks and steals must
represent
some study on run scoring. The AB-H is effectively the outs the player
cost the team.
 
It seems to be a good measure... although the number resulting doesn't
seem to mean
much - neither does slugging percentage when you think about it. I would
rather see
the denominator be plate appearances, with the ratio then meaning
something like
"expected runs created per plate appearance." You can't just multiply
the existing
ratio by 27 and get "expected runs per 9 inning game created by lineup
of 9 of these
players" since the coefficients should change when non-average players
bat (i.e., Bonds
would usually bat with more runners on base if his team was made up of 9
Bondsmen.

One adjustment I'd like to see in OPI is seeing CS drop to the
denominator. A CS is an
out created, and while it does reduce the number of current expected
runs in an inning, it also
reduces the player's contribution to the run total.
 
I have a problem with SBs and CSs being there as it is, since there
isn't a good way to measure
player speed - can he consistently go from first to third on a single to
right field, or score
from second on a dribbler which gets by the second baseman? Either
include baserunning or don't.
 
Another measure I'd like to see is bunt singles given a different
coefficient than singles which 
reach the outfield (or ones whjch are knocked down by infielders). And
while we're at it, fly-ball
outs, ground-ball outs and strikeouts all have different effects on run
potential. At least
subtract a little for each strikeout.
 
I'm sure all of this has been researched ad nauseum, and the formula
Kevin is using is an
approximation, so don't treat this as a flame..

==> Jim

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- Jim Gindin							 -		
- AIX Communications Software Development			 -
- I do not claim to speak for my company (or my country, or even -
- Dan Quayle) in this posting.					 -
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