# Re: st: Matrix manipulation.

 From Victor Mauricio Herrera <[email protected]> To [email protected] Subject Re: st: Matrix manipulation. Date Thu, 01 May 2008 23:55:57 -0500

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
(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.
>
>  of the coefficient matrix. In the example below you get the coefficient
>  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 southXnoncoll = south*noncoll
>  gen ln_w = ln(wage)
>  *------------ 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
>
>  Buitenveldertselaan 3 (Metropolitan), room Z434
>
>  +31 20 5986715
>
>  http://home.fsw.vu.nl/m.buis/
>  -----------------------------------------
>
>
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