topic Re: Quadratic Regression Fit in Discussions

Quadratic Regression Fit - Please Help

briankulp1_gmai — Thu, 12 Nov 2015 18:46:04 GMT

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

Re: Quadratic Regression Fit

Kevin_Anderson — Thu, 12 Nov 2015 18:54:30 GMT

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.

Re: Quadratic Regression Fit - Please Help

briankulp1_gmai — Thu, 12 Nov 2015 20:17:44 GMT

Thanks Kevin! Exactly what I was looking for!