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MathGroup Archive 2007

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Re: Curve-fitting/data analysis question...

  • To: mathgroup at smc.vnet.net
  • Subject: [mg73359] Re: Curve-fitting/data analysis question...
  • From: "Robert Dodier" <robert.dodier at gmail.com>
  • Date: Wed, 14 Feb 2007 05:14:59 -0500 (EST)
  • References: <200702110615.BAA11578@smc.vnet.net><eqsa48$jn0$1@smc.vnet.net>

sherifffruitfly wrote:

> For each point p in my interval, I constructed two models - a linear
> one using the points to the LEFT of p, and an exponential one using
> the points to the RIGHT of p. I ran chi-squared to see which model p
> belongs to. At the beginning, LEFT wins pretty much every time. When
> RIGHT started winning is where I called the cut-off.

Better still would be to choose the cut-off point to minimize the sum
of the goodness of fit (i.e., chi-square) on both sides.
(It's not a question of which side fits better, but rather how to get
better fit overall.) Maybe you're already doing that; I can't tell for
sure.

I would be interested to hear whether the total chi-square is
sensitive
to the placement of the cut-off point. Do you find that there is one
point which is much better than the rest, or is there a range of
points which are all more or less OK?

HTH
Robert Dodier



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