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st: 2 elasticity questions


From   "Botelho, Delane" <delane.botelho@marshall.usc.edu>
To   "'statalist@hsphsun2.harvard.edu'" <statalist@hsphsun2.harvard.edu>
Subject   st: 2 elasticity questions
Date   Fri, 19 Jul 2002 18:11:02 -0700

Hi

I ran "xtlogit" (random effect) and "mfx compute, eyex" to get the
elasticities. Then I calculated the same elasticities using "predict var,
pu0" and plugging in the formula of elasticities of logit (p. 111 Ben-Akiva
& Lerman). Fortunately I got the same results, and I understood what STATA
did.

Then, I ran "regress" (another dataset, different variables), using natural
logs of quantity (depvar) and price (varlist). The coefficient of price is
supposed to be the elasticity. But when I ran "regress" not using natural
logs, and afterwards "mfx compute, eyex", those elasticities are not the
same as the coefficients in the first regression. 

My 2 questions are:
1. I know how STATA is calculating elaticity in the Logit model, but how
(which formula) is STATA calculating the elasticity in the "regress" case?
2. I also need to run Poisson regression and calculate elasticities. If I
use "mfx compute, eyex" after "poisson", how (which formula) STATA will
calculate the elasticity?

Please, give at least some reference.

Thanks

Delane Botelho




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