st: oaxaca decomposition

["Andrey V. Ivanov" <aivanov@rumms.uni-mannheim.de>]

Dear all,

I am trying to use Oaxaca-type decomposition of a wage equation with  
selection effects, as discussed in Neuman and Oaxaca, "Estimating labor  
market discrimination with selectivity-corrected wage equations:  
methodological considerations and an illustration from Israel", discussion  
paper 2-2003 from the Pinhas Sapir Center for Development at Tel-Aviv U.

It seems that all the standard decomposers (like oaxaca) in Stata adjust  
the wage equations for selectivity, and then decompose the adjusted  
difference into explained and unexplained effect.

Say, I have the following model:

y1 = x1b1 + s1c1
y2 = x2b2 + s2c2,

where s is the selection variable. Then, the standard Stata procedure  
would do the following, as far as I understand:
adjust y1-y2 with s1c1 - s2c2, and then decompose this adjusted difference  
into:

(x1 - x2)b1 + x2(b1-b2)

However, as in the above paper, I want to have three decomposition terms:

(x1 - x2)b1 + x2(b1-b2) + (s1c1 - s2c2),

such that I can further decompose the selection term, (s1c1 - s2c2). This  
involves calculating s0 = f(h2g1)/F(h2g1), where g1 is the estimated  
parameter from the selection model of the sample 1 and h2 are the  
characteristics that enter the selection model for sample 2, F is normal  
CDF and f is normal PDF. (see paper above, pp. 5 and 8)

Could anyone assist me with how to calculate this f/F ratio in stata?

Thanks
andrey v. ivanov

--
Chair for Applied Microeconomics, Department of
Economics, Mannheim University, D-68131 Mannheim, Germany
Website: http://www.vwl.uni-mannheim.de/gk/_ivanov/
Co-editor of JEPS: http://jeps.repec.org/

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