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st: 2 limit tobit in system of demand equations


From   Brunetti Mike <bruno49_99@yahoo.com>
To   statalist@hsphsun2.harvard.edu
Subject   st: 2 limit tobit in system of demand equations
Date   Tue, 3 Jun 2003 12:25:53 -0700 (PDT)

Stata users:

I was wondering if there was a command in stata, or
possibly, an .ado file that can estimate a system of
demand equations with censoring on both sides. 
Specifically, I am trying to estimate a system of 2
demand equations which are censored at 0 and 1. 

I know that I can estimate a single equation using the
“tobit” command but how can I estimate two equations
simultaneously? 

Here is the model I would like to estimate:
For 3 goods the observed expenditure share on each is:
C, S, H

C* and S* represent the desired expenditure share on
each good:
C*=Xb1+e1
S*=Xb2+e2
Where X is a matrix of variables, b1 and b2 are
coefficients, and e1 and e2 are errors.

The system is defined as:
C=	0       if C*<=0
        C*      if 0<C*<1
        1       if C*>1

S=	0       if S*<=0
	S*      if 0<S*<1-C
	1-C     if S*>1

H=1-C-S

The equations for C and S are each two limit tobits.
But estimating this system simultaneously is
complicated.  Any help or suggestions would be greatly
appreciated. 

Thanks a lot.
Mike 


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