From: niguma@ug.cs.dal.ca (Gordon Niguma)
Subject: The Lies Of E.R.A. With Small Samples
Organization: Math, Stats & CS, Dalhousie University, Halifax, NS, Canada
Distribution: na
Date: Fri, 20 Nov 1992 01:34:56 GMT

  Usually E.R.A. will somehow correlate with the performance of a pitcher     
allowing hits per 9, bb per9ip etc. However, sometimes in small 40 to perhaps
as high as 80 innings pitched, pitchers will drastically differ in what their
ERA is. Take the following sample (I prorated one guy from 41 2/3 innings
to twice that amount):

            IP  H  BB  SO  2B  3B  HR  H/9  BB/9  K/9  SB-CS  BA  OBA  SLG
PITCHER A   83 74  38  62   8  0   10  8.0  4.1   6.7   10-4 236  316  357
PITCHER B   88 80  27  47   8  1    8  8.2  2.8   4.8    2-4 249  314  355

Yet in the ERA category we see that PITCHER A registered a 5.18 ERA while
PITCHER B filled in at 2.34 ERA. Subtracting the ERA from the statistical
picture probably makes PITCHER A the better, more powerful pitcher, someone
you'd rather close with or at least making it a very close decision.
  But as we speak PITCHER A is trying to hang on to a major league job while
PITCHER B is the closer for another team (Both American League). Anyone
hazard a guess to who they are?
  How can this happen? Well, these are reliever ERA's so we know that often
the inherited runners that a pitcher allows in will not affect his ERA.
PITCHER B came in with 60 IR while stranding 49 of them. PITCHER A had  
only 16 (prorated) IR while stranding 10 of them. So clearly PITCHER B's hits
hurt his teammates ERA and not only his own. This is a HUGE factor but
can it really account for a difference of almost 3.00 ER per 9ip?
  Another factor maybe the ability of PITCHER B to produce a groundball which
his fielders turn to a deuce behind him. This would dramatically affect ERA's.
Another maybe the "clutch" ability of PITCHER B who happened (by luck or
ability to "bear down" ie Jack Morris) to avoid that hit with a runner at
third and save his ERA.
Anyways, what does this imply about the data? Chances are that alot of this
is EXTREME dumb luck; that if you run these stats through a simulator, the
differences would very rarely by this wide. It may be dangerous to state
but can this imply that:

    a) batters, over 177 PA, be strong hitters despite poor OPS numbers by
outstanding clutch performances and ability to avoid a double play?
    b) vice versa?

  I mentioned appplying the Runs Created Formula to pitchers to generate an
expected ERA but was told that this was not effective (I think Valentine
mentioned this point). I'm not exactly sure why this is so, is it because
a pitcher is a factor in many consecutive batters in a row and thus their
ability to induce a DP ball or to avoid a big inning by allowing minimal
power, while batters since they are only 1/9 of the puzzle must consistently
maximize their offensive strengths? What if we did try predicting team ERA
by using the Runs Created Formula for hitters? Would their be a strong         
correlation? Would their be pitchers who could consistently do better than
their implied Runs Created ERA?
  Just some things to think about.....

					Gord Niguma
					(fav player: John Olerud)