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st: RE: RE: what does it mean the default for -mfx- is discrete when it is evaluated at the mean?


From   "Martin Weiss" <martin.weiss1@gmx.de>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: RE: RE: what does it mean the default for -mfx- is discrete when it is evaluated at the mean?
Date   Tue, 1 Jun 2010 23:39:52 +0200

<>

This was a knee-jerk reaction of course, since in a linear regression the
marginal effects would always be constant.

Still, what is the problem with saying that the marginal effect displayed is
for going from zero to one, i.e. the only move that a dummy can possibly
make? The fact that the share of ones in your sample is 37% does not change
this fact, does it?


HTH
Martin


-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu
[mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Martin Weiss
Sent: Dienstag, 1. Juni 2010 23:27
To: statalist@hsphsun2.harvard.edu
Subject: st: RE: what does it mean the default for -mfx- is discrete when it
is evaluated at the mean?


<>

The point of evaluation does not seem to matter at all in this code, though:


***********
sysuse auto, clear
reg price weight length foreign
mfx compute, dydx at(mean foreign=0)
mfx compute, dydx at(mean foreign=1)
mfx compute, dydx at(mean foreign=.2)
mfx compute, dydx at(mean foreign=.5)
mfx compute, dydx at(mean foreign=.8)
***********


HTH
Martin


-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu
[mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Nirina F
Sent: Dienstag, 1. Juni 2010 16:09
To: statalist@hsphsun2.harvard.edu
Subject: st: what does it mean the default for -mfx- is discrete when it is
evaluated at the mean?

Hello,
I have a dummy for dependent and main independent variable. I am using
ivprobit.
When I try to get the marginal effects, mfx  shows you that the
default setting is 'discrete', that is, evaluate the marginal effect
of a dummy going from 0->1. But it is evaluated at the mean (and under
x it shows 0.37 for the independent variable) so I am a little bit
confused about the interpretation of the marginal effect.
Thank you for your help.
Nirina
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