Marteen's suggestion is well appreciated. However, variables defined in this way tend to be collinear and are dropped from the regression model, leading to non-existing coefficients and non-conformable matrices.
Thanks,
VICTOR M. HERRERA
PhD., Student
Population Health Sciences
University of Wisconsin
610 Walnut St. 632 WARF
Madison, WI 53726
(608) 265-3686
----- Original Message -----
From: Maarten buis <[email protected]>
Date: Thursday, May 1, 2008 2:07 pm
Subject: Re: st: Matrix manipulation.
To: [email protected]
> --- Victor Mauricio Herrera <[email protected]> wrote:
> > I'm running a regression model and then using the matrix of
> > coefficients e(b) for additional calculations. In the model I have
> an
> > interaction term between two dichotomous variables (i.e.
> > gender-by-obesity, with women coded as 0 and men coded as 1). The
> > coefficient for obesity in women is already in e(b) but not the
> > coefficient for obesity in men. I know I can easily calculate this
> > coefficient using lincom, but the problem is that I need to add the
> > coefficient for obesity in men as an additional column to the e(b)
> > matrix, to be able to do additional calculations using e(b). In not
> > very familiar with matrix manipulation and I wonder if there is an
> > easy way to do this.
>
> The best way is to change the variables you add to your model instead
> of the coefficient matrix. In the example below you get the coefficient
> of south (in your case obesity) for college graduates (in your case
> women) in the coefficient of southXcollgrad, and the coefficient of
> south of non-college graduates (in your case men) in the coefficient
> of
> southXnoncoll. Notice that in this case we leave out the main effect
> of
> south (in your case obesity).
>
> Hope this helps,
> Maarten
>
> *------------ begin example ------------
> sysuse nlsw88, clear
> gen noncoll = !collgrad
> gen southXcollgrad = south*collgrad
> gen southXnoncoll = south*noncoll
> gen ln_w = ln(wage)
> reg ln_w southXcollgrad southXnoncoll collgrad noncoll, nocons
> *------------ end example ---------------
> (For more on how to use examples I sent to the Statalist, see
> http://home.fsw.vu.nl/m.buis/stata/exampleFAQ.html )
>
> -----------------------------------------
> Maarten L. Buis
> Department of Social Research Methodology
> Vrije Universiteit Amsterdam
> Boelelaan 1081
> 1081 HV Amsterdam
> The Netherlands
>
> visiting address:
> Buitenveldertselaan 3 (Metropolitan), room Z434
>
> +31 20 5986715
>
> http://home.fsw.vu.nl/m.buis/
> -----------------------------------------
>
>
> ___________________________________________________________
> Yahoo! For Good. Give and get cool things for free, reduce waste and
> help our planet. Plus find hidden Yahoo! treasure
>
> http://green.yahoo.com/uk/earth-day/
> *
> * For searches and help try:
> * http://www.stata.com/support/faqs/res/findit.html
> * http://www.stata.com/support/statalist/faq
> * http://www.ats.ucla.edu/stat/stata/
>
*
* For searches and help try:
* http://www.stata.com/support/faqs/res/findit.html
* http://www.stata.com/support/statalist/faq
* http://www.ats.ucla.edu/stat/stata/
