Hi Dave,
thanks for the hint. Now the terms remain in the regression. But I am sill unsure about the interpretation. How does that change when the polynomial terms are centred?
Best Phil
-------- Original-Nachricht --------
> Datum: Mon, 13 Jul 2009 12:53:57 -0500
> Von: David Airey <[email protected]>
> An: Statalist <[email protected]>
> Betreff: re: st: STATA drops squared terms from the model
> .
>
> Does centering before making the polynomial terms help?
>
> -Dave
>
>
> > Dear Statalist, I estimate a log-log model with interaction term of
> > the following form: lnY = b0 + b1lnX + b2lnZ + b3lnX*lnZ + e I want
> > to test whether X and Z have a nonlinear effect on Y. Therefore, I
> > add squared terms of X and Z to the model. When I estimate this
> > model STATA drops X and Z from the model due to multicollinearity.
> > The correlation coefficients between the unsquared and squared terms
> > are very high (> 0,96). I have some problems interpreting this
> > result. Does this mean that there is no non-linear effect? Best
> > regards Phil
> >
> *
> * 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/
--
GRATIS für alle GMX-Mitglieder: Die maxdome Movie-FLAT!
Jetzt freischalten unter http://portal.gmx.net/de/go/maxdome01
*
* 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/
