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st: RE: saving coefficient matrix for two models

From   "Michael Palmer" <>
To   <>
Subject   st: RE: saving coefficient matrix for two models
Date   Wed, 23 Feb 2011 16:00:21 +1100

Dear all, 

I'm estimating a two part model (first part logit, second part log
linear model) and am calculating the marginal effects which require
coefficients from both models. The question is how to save coefficients
from the two consecutive models. 
For example.. 

Logit hospital_visit $xlist
Mat b = e(b)

Reg Ln_hospital_expenditure $xlist
Mat b = e(b)

I presume 'display _b[age]' for example will give me the coefficient for
second model but how to derive the same coefficient from the first
model. Note the independent variables are the same for each model. I
suppose I could rename the variables in the second model but hoping
there is a simpler way. 

Any help would be appreciated. 

Many thanks, 


Michael Palmer
PhD Candidate 
National Centre for Epidemiology and Population Health 
The Australian National University 
Ph. 6125 0538
M. 0437 867 940

-----Original Message-----
[] On Behalf Of Maarten buis
Sent: Thursday, 3 February 2011 7:54 PM
Subject: RE: st: FW: Marginal effects for the two-part model

--- On Thu, 3/2/11, Michael Palmer wrote:
> There seems to be some confusion on the computation of marginal 
> effects for the TPM I described as some authors still suggest combined

> marginal effects.

That depends on what the outcome of interest is. If you want the
unconditional outcome, for example people get 0 cost when they don't
seek medical help and some positive cost when they do, then you need to
include both parts of your model. However, as I understood your original
question, you wanted the cost conditional on seeking medical help.

Hope this helps,

Maarten L. Buis
Institut fuer Soziologie
Universitaet Tuebingen
Wilhelmstrasse 36
72074 Tuebingen


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