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st: Krinsky and Robb procedure

From   German Muchnik Izon <[email protected]>
To   [email protected]
Subject   st: Krinsky and Robb procedure
Date   Fri, 22 Aug 2008 17:54:57 -0600

Hi all,

I have a new question. I am estimating 95% confidence 
intervals for willingness to pay (WTP) for a good using a 
command called wtpcikr that implements the Krinsky and 
Robb procedure, recently developed by P. Wilner Jeanty for 
stata. Based on a power point presentation given by Jeanty 
at the 6th North American Stata Users Group Meeting 2007, 
the steps of this procedure is as follows:

1.Estimate the WTP model of interest
2.Obtain the vector of parameter estimates     and the 
variance-covariance (VCV) matrix
3.Calculate the Cholesky decomposition, C, of the VCV 
matrix such that
4.Randomly draw from standard normal distribution a vector 
x with k independent elements
5.Calculate a new parameter vector Z such that
6.Use the new parameter vector Z to calculate the WTP 
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 observations

The example given in this presentation is:

drop _all
. set memory 8m
. use south
. gen lbid=ln(bid)
. probit ypay lbid unlimwat govtpur environ waterbill 
. wtpcikr lbid unlimwat govtpur environ waterbill urban, 
reps(50000) meanl expo

Is there a way in stata to obtain a vector of the mean 
WTP's that are estimated in step 6 after each replication.

Thank you!!


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