Re: st: RE: areg/xtreg

[Terra Curtis <terra.curtis@cambridgefinance.com>]

Yes, I did try that.  I took the constant into account by subtracting 
from the dependent variable average.  So, I had three ratios:
(1) [coef1*indvar1(avg) ] / (depvar(avg)-const)
(2) [coef2*indvar2(avg) ] / (depvar(avg)-const)
(3) [coef3*indvar3(avg) ] / (depvar(avg)-const)

It is my understanding that these three ratios should add to 1. However, 
the calculation of coefficients times means plus constant (as you have 
specified as x1 below) does not produce a value which is equal to the 
mean of my dependent variable.

Scott Merryman wrote:

> Did you add in the constant?
>
> . webuse grunfeld,clear
>
> . qui areg invest kstock mvalue, ab(com)
>
> . qui sum kstock
>
> . local ks = r(mean)
>
> . qui sum mvalu
>
> . local mv = r(mean)
>
> . qui sum invest
>
> . local x1 = (_b[kstock]*`ks' + _b[mvalue]*`mv' + _b[_cons])/r(mean)
>
> . disp "`x1'"
> .999999999999999
>
> Scott
>
>
>   
> > -----Original Message-----
> > From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-
> > statalist@hsphsun2.harvard.edu] On Behalf Of Terra Curtis
> > Sent: Monday, March 06, 2006 1:35 PM
> > To: statalist@hsphsun2.harvard.edu
> > Subject: st: areg/xtreg
> >
> > I am using Stata 8.2.  I have a question regarding what is written in
> > the Stata manual for -areg-.  The manual reports that "-areg- identifies
> > the model by choosing the intercept that makes the prediction calculated
> > at the means of the independent variables equal to the mean of the
> > dependent variable: y(hat)=x(hat)*beta"
> >
> > I have used this fact to try to calculate the "percent of mean
> > explained" by each independent variable in my regression.  For
> > concreteness, I have regressed like this:
> >
> > areg depvar indvar1 indvar2 indvar3, absorb(timevar)
> >
> > For the percent of mean explained calculation, I have taken each
> > coefficient multiplied by the mean of that independent variable and
> > divided by the mean of the dependent variable.  After I have done this
> > for all three independent variables, in theory the three percentages
> > should add up to 1.  However, this is not the case.  Can anyone see why
> > not?
> >
> > Thank you,
> > Terra Curtis
> >     
>
>
> *
> *   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/