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Re: st: how to access e(b) and e(V)


From   Philomela@gmx.net
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: how to access e(b) and e(V)
Date   Tue, 20 Oct 2009 14:20:52 +0200

Thank you very much for all your comments- 
Your really helped me a lot!

-------- Original-Nachricht --------
> Datum: Tue, 20 Oct 2009 04:36:59 -0700 (PDT)
> Von: Maarten buis <maartenbuis@yahoo.co.uk>
> An: statalist@hsphsun2.harvard.edu
> Betreff: Re: st: how to access e(b) and e(V)

> --- On Tue, 20/10/09, Philomela@gmx.net <Philomela@gmx.net> wrote:
> > Actually i would like to come up with a linear demand
> > function like that:
> > Consumption= constant+ beta_1*Price+beta_2*Income+ ...
> > and a loglog demand function.
> > I used the spreadheet programm and manually calculated
> > Consumption for various prices and got the two demand
> > functions from that, but unfortunatly, due to the log
> > transformation i have the following problem:
> > exp(E(ln(Consumption))) is not equal to E(Consumption).
> > I thought more precise estimates would help-but as it
> > turned out now- they don't.
> > So, can I  estimate the consumption for different
> > prices directly in Stata to get the demand functions?
> > Then, I should be able to deal with the retransformation
> > bias  as suggested in
> > Cameron&Trivedi(2009):Microeconometrics using Stata.
> 
> You have two options:
> 1) Use -glm- with a log link function, and after that
> you can just use -predict- to get the predicted values.
> So you would type something like:
> 
> glm consumption price income ... , link(log)
> predict consumptionhat, mu
> 
> 2) Alternatively the method proposed by Cameron & 
> Trivendi is implemented in Stata by Kit Baum as
> the -levpredict- package. You can install that
> by typing in Stata: -ssc install levpredict-.
> 
> IMHO the -glm- solution is more elegant as it tackles
> the problem at its root: In this case -glm- models 
> log(E(consumption)) while -regress- models 
> E(log(consumption)). Because of this the exponentiating
> the left hand side and right hand side after a -glm-
> model (which happens when you use -predict-, -adjust-,
> or specify the -eform- option) will lead to results
> in the original unit of consumption, where this is not
> true after -regress-. The solution offered by Cameron
> & Trivendi seems to me a bit of a post hoc solution.
> 
> -- Maarten
> 
> --------------------------
> Maarten L. Buis
> Institut fuer Soziologie
> Universitaet Tuebingen
> Wilhelmstrasse 36
> 72074 Tuebingen
> Germany
> 
> http://www.maartenbuis.nl
> --------------------------
> 
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> 
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