From: tamada@cheshire.oxy.edu (Michael K. Tamada)
Subject: Re: Phoenix is absolutely scary...
Organization: Occidental College, Los Angeles, CA 90041 USA.
Date: Mon, 4 Jan 1993 09:25:51 GMT

In article <43013@sdcc12.ucsd.edu> aminkoff@sdcc13.ucsd.edu (Tony Minkoff) writes:

>The best statistical measure of team defense that I can think of is
>opponents' points-per-possession.  "Possessions" are not listed in
>the boxscores, but can be approximated by (turnovers + field goals
>attempted - offensive rebounds + 0.4 * free throws attempted).
>
>(Note that I do not count an offensive rebound as the beginning of a
>new possession.  E.g., if a team shoots, misses, gets the offensive
>board, shoots again, and makes it, that counts as one possession,
>not two.)

     This is an excellent measure.  Two minor nitpicks:  0.4 seems a little
low for free throws.  Granted, .5 is too high, because some players shoot
free throws without using a possession, via 3-point plays or technical fouls.
I think .45 is a good estimate.
     
     Secondly, I prefer to count each grab of an offensive rebound (and for 
that matter, each steal from the opposition, and each basket made by the
opposition) as the start of a new possession.  Tony's incorporation of
offensive rebounding into points per possession gives us a literal measure
of a team's ability to score points.  Sounds great, but this implicitly
divides basketball into two categories:  offense and defense (with defense
having defensive rebounds incorporated into it).
     What's the alternative?  I prefer to divide basketball into 3
categories, not two.  I.e., basketball is not just offense and defense,
it's offense, defense, and rebounding.  
     Some examples where I think the 3-way distinction makes sense:  consider
a team of Moses Malones, they might shoot only 45% but by getting a ton
of rebounds they still score a lot.  Conversely, consider a team of Reggie
Millers; they'd shoot great but lacking the rebounding horses they wouldn't 
get many points off of second shots.  Overall, the two teams might score
about the same number of points, but by combining rebounding ability with
"true" scoring ability, we lose some ability to distinguish who's good at
what.
     Actually, to be fully accurate, offense really needs to be subdivided
into two categories:  shooting, and ball-handling (meaning not turning the
ball over).  Defense similarly needs to be subdivided into shooting defense,
and ball-hawking (getting steals and causing turnovers).  And of course
rebounding is subdivided into offensive and defensive rebounding.  And
somewhere in there ideally we'd like to have some measure of passing ability.
      Anyway, what this all means is that there is a range of stats we
can use:  win-loss record of course is the bottom line (possibly adjusted
for strength of schedule).  Win-loss record is strongly correlated with
points you score minus (or divided by) points you give up.  We could try 
calculate these points scored/points given up statistics by using points 
per possession and defensive points per possesion, with rebounds included
as Tony suggests. But these calculations wouldn't be entirely accurate because 
they don't give us a way of finding out how many possessions each team got.
     In contrast, defining points per possession without rebounds allows 
better measures of possessions:  posessions obtained by rebounds, steals,
and opponent baskets.

>Maybe sometime in the next week, if I have time, I will actually
>calculate the opponents'-points-per-possession (OPPPPP?) stat for
>each team for last year.  (I don't think I have current data
>available.  If somebody can provide me with it, I'd be most
>appreciative.)

      Sorry, I don't have 'em.  The USA Today gives great individual stats, 
but incomplete team stats.  Don't know where to get complete team stats...
maybe The Sporting News?
--------------------------------------------------------------------------
  |__	       o
  | W			   Mike Tamada
		  |\	   Institutional Research Office
		   \O	   Occidental College
		    |      tamada@oxy.edu
		   /|
		  | |

Newsgroups: rec.sport.basketball.pro