Monday, March 06, 2006

Re: st: RE: areg/xtreg

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/


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