Re: st: Krinsky and Robb procedure

[Martin Weiss <martin.weiss@uni-tuebingen.de>]

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 afterwards.

HTH
Martin





Quoting German Muchnik Izon <german@unm.edu>:


> 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
> urban
> . 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!!
>
> German.
>
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