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st: RE: areg/xtreg


From   "Scott Merryman" <smerryman@kc.rr.com>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: RE: areg/xtreg
Date   Mon, 6 Mar 2006 14:41:18 -0600

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



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