Re: st: linear, quadratic terms and centering

["Michael N. Mitchell" <Michael.Norman.Mitchell@gmail.com>]

Dear Fabio

  You were correct when you wrote...

Or do I first center the linear term and calculate the square term on the basis of the 
"centered" linear term ?

  Or, in Stata, you can do this (say you want to center -x- around 100)...

generate xcentered = x - 100
regress y c.xccentered##c.xccentered

  That -regress- command will include -xcentered- as well as the squared term.

Hope this helps,

Michael N. Mitchell
Data Management Using Stata      - http://www.stata.com/bookstore/dmus.html
A Visual Guide to Stata Graphics - http://www.stata.com/bookstore/vgsg.html
Stata tidbit of the week         - http://www.MichaelNormanMitchell.com



On 2010-08-21 12.40 AM, Fabio Zona wrote:
> Dear Statalist,
>
> a very simple question: I have
>
> y = c + x0 + x1 + x1square
>
> In order to center x1 and x1square, do I first need to calculate the square term and afterwards to center both the linear and the quadratic term around their respective means?
> Or do I first center the linear term and calculate the square term on the basis of the "centered" linear term ?
>
> I guess that the first alternative works.
>
> Thanks
>
> *
> *   For searches and help try:
> *   http://www.stata.com/help.cgi?search
> *   http://www.stata.com/support/statalist/faq
> *   http://www.ats.ucla.edu/stat/stata/
*
*   For searches and help try:
*   http://www.stata.com/help.cgi?search
*   http://www.stata.com/support/statalist/faq
*   http://www.ats.ucla.edu/stat/stata/