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st: Re: RE: RE: mfx after xtnbreg and how to compute predicted Y


From   "Martin Weiss" <[email protected]>
To   <[email protected]>
Subject   st: Re: RE: RE: mfx after xtnbreg and how to compute predicted Y
Date   Sun, 19 Oct 2008 21:06:10 +0200

The additional x-column gives the means of the covariates at which the marginal effect is estimated.

*********
webuse airacc, clear
xtnbreg i_cnt inprog, exposure(pmiles) irr
mfx
*let´s see the mean of "inprog" from the "x-column"
su inprog,mean
di in red r(mean)
*********

-mfx evaluates at the mean as default. See -help mfx##atlist-

HTH
Martin

----- Original Message ----- From: "Pek-Hooi Soh" <[email protected]>
To: <[email protected]>
Sent: Sunday, October 19, 2008 8:47 PM
Subject: st: RE: RE: mfx after xtnbreg and how to compute predicted Y


Hi Nick,

I was told that the coefficients of non linear models cannot be used
directly for interpretation, and I should use mfx that give the marginal
effects (exp(B),I think). In the table, the dydx column output is the same
as the coefficients of xtnbreg, the x column is the only extra information.
What is x?

Cheers,

Pek


-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Nick Cox
Sent: October-19-08 11:21 AM
To: [email protected]
Subject: st: RE: mfx after xtnbreg and how to compute predicted Y

-mfx- is giving you extra information for the model you just ran.

The help for -xtnbreg postestimation- indicate how to get predictions in
Stata. There is no need to resort to any other software.

Nick
[email protected]

Pek-Hooi Soh

I have a count panel data model with interaction terms where the terms
are mean centered.

I estimated the full model by -xtnbreg- and ran -mfx-. The marginal effect
table presents the same coefficients and standard errors as the table for
-xtnbreg-. Is this possible?

If I do get the correct -mfx- output, how do I compute predicted Y? Do I
have
compute y = exp(XB) where B stores marginal effects separately in Excel ?

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