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

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• Oct 15, 2002
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> [...]
>
> > I once compared the normal probability approach to different
> > pythagorean exponents and the normal approach is always better.
Not
> > by enough to worry about, though. I'd expect any linear form or
> > ratio to be similar to the pythagorean. Since the normal
approach
> > takes into account a little more than just points scored and
points
> > allowed (how variable they were in doing so), it should be a
little
> > more accurate. It also allows it to work without modification in
any
> > league, whereas you need to change the exponent on the
Pythagorean
> > approach from the WNBA to the NBA to college men to college women
to
> > HS, etc.
>
> Good points. What is both a strength and weakness of the normal
make more
> accurate predictions. But one needs to have data on, not just the
mean
> points, but also the variance of points (and I think your formula
takes
> 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
matters.

DeanO

> 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
and
> allowed.
>
> As usual, there's a choice of the quick-and-dirty vs the more-
accurate-
> but-more-work calculations.
>
>
> --MKT
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