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Nov 12, 2015 10:46 AM
(6130 views)

Hello,

When I perform a quadratic regression, it returns the form y=a+bx+c(x-d)^2. I would like it in the form y=a+bx+cx^2 so that I can have the correct parameter estimates. How can I do this - either change the way the model returns or change the parameters as needed?

Thanks,

Brian

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Hi, Brian!

Try using the Fit Special... dialog of the Fit Y by X platform (Under the LIRT by Bivariate Fit).

Leave both Y and X as No Transformation, specify the degree as 2 Quadratic, and uncheck the Centered Polynomial checkbox. That will give you the model you seek.

As an aside, JMP almost always centers the variables in analyses since it makes a lot of statistical sense (makes parameters comparable, etc.).

As another, more distant, aside LIRT stands for Little Inverted Red Triangle.

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Hi, Brian!

Try using the Fit Special... dialog of the Fit Y by X platform (Under the LIRT by Bivariate Fit).

Leave both Y and X as No Transformation, specify the degree as 2 Quadratic, and uncheck the Centered Polynomial checkbox. That will give you the model you seek.

As an aside, JMP almost always centers the variables in analyses since it makes a lot of statistical sense (makes parameters comparable, etc.).

As another, more distant, aside LIRT stands for Little Inverted Red Triangle.

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Re: Quadratic Regression Fit - Please Help

Thanks Kevin! Exactly what I was looking for!