quadratic regression

[jimjohn]

can someone plz tell me how to do multiple regression where one of my indep variables is related to y in a quadratic way. so my regn equation would be like:
y = b0 + b1 * X1 + b2 * X2 + b3 * (X3 ^ 2)

thanks!

[Swank, Paul R]

You don't want x3**2 without x3 also. And, depending on the range of x3,
x3**2 can be highly correlated with X3**2 so you may want to center X3
(X3 - mean(X3)) first.

Y = b0 + b18x1 + b2*x2 +b3*(X3-mean(X3)) + b4*(X3 - mean(X3))**2

Paul R. Swank, Ph.D.
Professor and Director of Research
Children's Learning Institute
University of Texas Health Science Center - Houston


-----Original Message-----
From: SPSSX(r) Discussion [mailto:[hidden email]] On Behalf Of
jimjohn
Sent: Tuesday, February 26, 2008 2:35 PM
To: [hidden email]
Subject: quadratic regression

can someone plz tell me how to do multiple regression where one of my
indep
variables is related to y in a quadratic way. so my regn equation would
be
like:
y = b0 + b1 * X1 + b2 * X2 + b3 * (X3 ^ 2)

thanks!
--
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