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From |
German Muchnik Izon <german@unm.edu> |

To |
statalist@hsphsun2.harvard.edu |

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. Best, German. ----------------------------- Germán M. Izón Department of Economics PhD. Candidate The University of New Mexico Ph# (505) 277-1951 --- On Sat, 8/23/08, Martin Weiss <martin.weiss@uni-tuebingen.de> wrote: From: Martin Weiss <martin.weiss@uni-tuebingen.de> Subject: Re: st: Krinsky and Robb procedure To: statalist@hsphsun2.harvard.edu 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 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. > > * > * For searches and help try: > * http://www.stata.com/help.cgi?search > * http://www.stata.com/support/statalist/faq > * http://www.ats.ucla.edu/stat/stata/ > * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/ * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

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