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Re: st: Heckman and Oaxaca


From   daneshva@ccmail.nevada.edu
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Heckman and Oaxaca
Date   Thu, 28 Oct 2004 07:12:03 -0700

Natalia,

There is no problem with dummies in a Heckman equation and "decomp."
decomp uses the mean of the variable, in this case the proportion of the
sample with dummy variable equal to one, and multiplies it by the
respective coefficient.  To see the details of the calculations, use can
use "himod, ds" and "lomod, ds."  this will give you the contribution of
each variable to the total endowment and the total residual.

It is possible to get high percentages (-301.0).  It means that the group
that you are using as the "low" or discriminated group actually has
advantage over the "high" group.  The commend, "himod, ds" or "lomod, ds"
will reveal what variables are the cause of high percentages.


Nasser


                                                                                                                                       
                      "Natalia Ferreira"                                                                                               
                      <nat6672@hotmail.com>             To:      statalist@hsphsun2.harvard.edu                                        
                      Sent by:                          cc:                                                                            
                      owner-statalist@hsphsun2.         Subject: st: Heckman and Oaxaca                                                
                      harvard.edu                                                                                                      
                                                                                                                                       
                                                                                                                                       
                      10/27/2004 05:04 p.m.                                                                                            
                      Please respond to                                                                                                
                      statalist                                                                                                        
                                                                                                                                       
                                                                                                                                       




Hi everybody

    I´m estimating a Heckman wage equation to migrants and not migrants,
and
after all I want to compare them by a Oaxaca decomposition, but I have a
question: there is any problem if my Heckman equation have some dummies?
How
"decomp" command deal with the dummies variables? Does it take means of
zeros
and ones? The results of my "decomp" give me discrimation % of -301.0
(D/R).
The % should not be between 0-100? The results are below:


Summary of decomposition results (as %)
-------------------------------------------
Amount attributable:             |    -10.3
- due to endowments (E):         |      5.2
- due to coefficients (C):       |    -15.5
Shift coefficient (U):           |     11.6
Raw differential (R) {E+C+U}:    |      1.3
Adjusted differential (D) {C+U}: |     -3.9
---------------------------------+---------
Endowments as % total (E/R):     |    401.0
Discrimination as % total (D/R): |   -301.0
-------------------------------------------

Thanks for the help, Natalia B.
________________________________
Pós Graduação IPE/USP

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