Re: st: margins, eyex

[Antoine Terracol <Antoine.Terracol@univ-paris1.fr>]

That's because when you regress ln(y) on ln(x), you assume a constant 
elasticity, i.e. a linear relationship between ln(x) and ln(y); 
estimated by the coefficient of ln(x).
When you regress y on x, you assume a linear relationship between x and 
y. The estimated relationship between ln(x) and ln(y) will not be linear 
in that case; and the elasticity will thus vary according to the value of x.


tl;dr: -reg y x- and -reg ln(y ln(x)- do not make the same assumptions 
on the relationship between y and x

Antoine

On 23/09/12 20:59, albert Lee wrote:
> Hi, I ran a simple OLS and invoked the margins, eyex(*) to calculate
> the elasticities.  I try to replicate the elasticity estimates by
> running the sample regression with logged dependent variable, and
> independent variables.  I was surprised that the coefficient estimates
> from the logged regression are not identical with the margins
> estimates.  Initially, I thought the discrepancies are due to atmeans
> and asobserved options with margins.  But I tried both options and
> still cannot replicate elasticity estimates by the logged regression.
> Could someone explain?
>
> Thanks,
>
> Albert.


--
Ce message a ete verifie par MailScanner
pour des virus ou des polluriels et rien de
suspect n'a ete trouve.

*
*   For searches and help try:
*   http://www.stata.com/help.cgi?search
*   http://www.stata.com/support/statalist/faq
*   http://www.ats.ucla.edu/stat/stata/