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1382Re: predicting W-L record based on team point differential

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  • Dean Oliver
    Oct 15, 2002
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      --- In APBR_analysis@y..., "Michael K. Tamada" <tamada@o...> wrote:
      > [...]
      > > I once compared the normal probability approach to different
      > > pythagorean exponents and the normal approach is always better.
      > > by enough to worry about, though. I'd expect any linear form or
      > > ratio to be similar to the pythagorean. Since the normal
      > > takes into account a little more than just points scored and
      > > allowed (how variable they were in doing so), it should be a
      > > more accurate. It also allows it to work without modification in
      > > league, whereas you need to change the exponent on the
      > > approach from the WNBA to the NBA to college men to college women
      > > HS, etc.
      > Good points. What is both a strength and weakness of the normal
      > probability approach is: it uses more information and thus can
      make more
      > accurate predictions. But one needs to have data on, not just the
      > points, but also the variance of points (and I think your formula
      > covariance into account too?). These are very easy calculations,

      Yup. The covariance is actually quite important. It shows how much
      teams play up or down to opponents. Teams definitely play up or down
      to opponents in the NBA. Not as clear in other leagues (or other
      sports). Basically there is no reason to blow a team out by 45 when
      you can win by 10 safely. That's also why you can't do a correlation
      of Jordan's minutes to how well his team performed. If he's injured
      and plays 20 minutes, the team could do poorly. But if he plays so
      well that the team is up by 35 after 20 minutes and he doesn't play
      again, the team can do well. I tried correlating playing time to
      team success (by game, not by season) and found this to be an
      impossible barrier to overcome. So, the correlation definitely


      > data are a bit less easy to get. Available, but a little more
      hunting and
      > a little more work to do, compared to just looking at points scored
      > allowed.
      > As usual, there's a choice of the quick-and-dirty vs the more-
      > but-more-work calculations.
      > --MKT
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