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st: mfx with tobit


From   Phil1899@gmx.de
To   statalist@hsphsun2.harvard.edu
Subject   st: mfx with tobit
Date   Wed, 04 Mar 2009 11:46:04 +0100

Hello,

I am running a regression model where the observations are censored from the left (at zero). Therefore, I use a Tobit model. Due to heteroskedasticity present in my data, I use the intreg command to obtain robust standard errors. However, I have two questions in this regard. 

First, the coefficients obtained from Tobit estimation cannot be directly interpreted. I found out that it is possible to use the mfx command to obtain the marginal effects and that different options exist to compute these effects; e.g. mfx, predict(e(0,1000)) or mfx predict(ystar(0,1000)). However, these commands lead to quite different results and I am not able to figure out which command is preferable in which situation?

Second, I have another dataset where the observations also pile up at zero, however, in this dataset the dependent variable does not only take on positive values, but sometimes also negative values. I am not sure which estimation technique is preferable in this case? 

I would appreciate any help,

best regards

Phil

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