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- Polynomial Fit Parameter Term Name Changes: Bug?

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Jun 4, 2013 10:53 AM
(628 views)

Hi,

I am writing a script that generates a second degree polynomial fit and then uses the parameter estimates in further calculations. My problem is the second order parameter estimate term name changes as a function of the input values, when it seems to me it should not. This term name change causes subsequent calculations to fail.

For example, the script below will generate a second degree polynomial fit with the following terms:

Intercept

height

(height-62.55)^2

My question is, why is the second order term name "(height-62.55)^2"? Shouldn't the term name be "height^2"? This name will change as a function of the input values. Is this a bug?

Any insights or workarounds are appreciated.

Thanks!

/*

bigClass=open("$SAMPLE_DATA/Big Class.JMP");

bigClass << Bivariate(

Y( :weight ),

X( :height ),

Fit Polynomial( 2, {Line Color( {213, 72, 87} )} )

);

*/

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Solution

By default JMP Bivariate Fit Polynomial generates a model with the terms of order 2 and greater centered around the mean of the X variable. It names the coefficients of those terms in a way that communicates what it did.

Instead use Fit Special, make sure neither X nor Y is transformed, change the degree to "2 quadratic" and uncheck "Centered Polynomial".

3 REPLIES

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Jun 4, 2013 10:59 AM
(540 views)

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By default JMP Bivariate Fit Polynomial generates a model with the terms of order 2 and greater centered around the mean of the X variable. It names the coefficients of those terms in a way that communicates what it did.

Instead use Fit Special, make sure neither X nor Y is transformed, change the degree to "2 quadratic" and uncheck "Centered Polynomial".

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Jun 4, 2013 1:25 PM
(540 views)