Bookmark and Share

Notice: On March 31, it was announced that Statalist is moving from an email list to a forum. The old list will shut down on April 23, and its replacement, statalist.org is already up and running.


[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

RE: st: RE: Interpretation of quadratic terms


From   Richard Williams <Richard.A.Williams.5@ND.edu>
To   "statalist@hsphsun2.harvard.edu" <statalist@hsphsun2.harvard.edu>, "statalist@hsphsun2.harvard.edu" <statalist@hsphsun2.harvard.edu>
Subject   RE: st: RE: Interpretation of quadratic terms
Date   Wed, 10 Mar 2010 08:40:46 -0500

At 07:34 AM 3/10/2010, Rodolphe Desbordes wrote:
Dear Rosie, Nick and Roger,

To conclude this thread and summarise the main arguments put forward by Nick, Roger and myself:

A) There can be some good reasons for "pre-emptive centering": a) to avoid computational issues, which are unlikely to arise with modern econometric softwares such as Stata; b) to provide substantive interpretation.

I agree with that, and I may add a sentence like that to my notes in the future! One other thought that I have had though: Suppose you are doing tests for collinearity and you have other variables in the model, so I use something like the -collin- command. Is there an advantage to minimizing the collinearity involving the variables that have the squared term? That is, would doing so make me better able to detect where the collinearity is among other variables? Or would it make no difference?

For example, suppose x1 is highly collinear with other variables. If I have x1^squared in the model, I am thinking I might miss the collinearity because x1 and x1^squared are so highly correlated (unless I have centered x1 first). This is just idle speculation on my part, I haven't fiddled around with it to see.


-------------------------------------------
Richard Williams, Notre Dame Dept of Sociology
OFFICE: (574)631-6668, (574)631-6463
HOME:   (574)289-5227
EMAIL:  Richard.A.Williams.5@ND.Edu
WWW:    http://www.nd.edu/~rwilliam

*
*   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/


© Copyright 1996–2014 StataCorp LP   |   Terms of use   |   Privacy   |   Contact us   |   Site index