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Re: st: Krinsky and Robb procedure

From   German Muchnik Izon <>
Subject   Re: st: Krinsky and Robb procedure
Date   Mon, 25 Aug 2008 08:33:04 -0600

Dear Martin,

Thank you so much for your suggestion. It works!!
Now I am going to see if I can program a convolution 
approach in stata to see if the median WTP I get for the 
two goods I included in my survey are statistically 
different from each other.


Germán M. Izón
Department of Economics
PhD. Candidate
The University of New Mexico
Ph# (505) 277-1951

--- On Sat, 8/23/08, Martin Weiss 
<> wrote:

     From: Martin Weiss <>
     Subject: Re: st: Krinsky and Robb procedure
     Date: Saturday, August 23, 2008, 11:45 AM

     Let me try an answer: if you look at the code of 
wtpcikr.ado, it calls
     -simulate- in line 57, saving into a -tempfile- with 
the option
     -saving(`simdat')-. I was able to turn this 
-tempfile- into a
     permanent one by appending the following after line 
134 (and saving
     wtpcikr.ado under a different name (wtpcikr2.ado)):

       u `simdat', clear
       save mysimdat

     This will allow you to access the meanwtp and the 
medianwtp from each
     simulation run


     Quoting German Muchnik Izon <>:

     > Hi all,
     > I have a new question. I am estimating 95% 
     > intervals for willingness to pay (WTP) for a good 
using a
     > command called wtpcikr that implements the Krinsky 
     > Robb procedure, recently developed by P. Wilner 
Jeanty for
     > stata. Based on a power point presentation given by 
     > at the 6th North American Stata Users Group Meeting 
     > the steps of this procedure is as follows:
     > 1.Estimate the WTP model of interest
     > 2.Obtain the vector of parameter estimates     and 
     > variance-covariance (VCV) matrix
     > 3.Calculate the Cholesky decomposition, C, of the 
     > matrix such that
     > 4.Randomly draw from standard normal distribution a 
     > x with k independent elements
     > 5.Calculate a new parameter
      vector Z such that
     > 6.Use the new parameter vector Z to calculate the 
     > measures of interest
     > 7.Repeat steps 4, 5, and 6 N(>=5000) times to 
obtain an
     > empirical distribution of WTP
     > 8.Sort the N values of the WTP function in 
ascending order
     > 9.Obtain a 95% confidence interval around 
mean/median by
     > dropping the top and bottom 2.5% of the 
     > The example given in this presentation is:
     > drop _all
     > . set memory 8m
     > . use south
     > . gen lbid=ln(bid)
     > . probit ypay lbid unlimwat govtpur environ 
     > urban
     > . wtpcikr lbid unlimwat govtpur environ waterbill 
     > reps(50000) meanl expo
     > Is there a way in stata to obtain a vector of the 
     > WTP's that are estimated in step 6 after each 
     > Thank you!!
     > German.
     > *
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