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From |
"P. Wilner Jeanty" <[email protected]> |

To |
[email protected] |

Subject |
st: Re: WTP from double bounded data |

Date |
Thu, 31 Jan 2008 16:42:37 -0500 |

On Jan 30, 2008 3:36 PM, Henrik Andersson <[email protected]> wrote: > Dear all, > > I have estimated a ml logistic model on double bounded WTP data. The > model I have estimated is an extension of the standard logit and it > looks as follows: > > * ml DB *** > > capture program drop double_cv > program double_cv > version 9.2 > args lnf xb bid > qui replace `lnf' = ln(invlogit($ML_y6*`bid'+`xb')) if $ML_y1 == > 1 > qui replace `lnf' = ln(invlogit(-($ML_y7*`bid'+`xb'))) if $ML_y2 > == 1 > qui replace `lnf' = ln(invlogit(-($ML_y6*`bid'+`xb')) - /// > invlogit(-($ML_y5*`bid'+`xb'))) if $ML_y3 == 1 > qui replace `lnf' = ln(invlogit(-($ML_y5*`bid'+`xb')) - /// > invlogit(-($ML_y7*`bid'+`xb'))) if $ML_y4 == 1 > end > > ** Estiamte model ** > > ml model lf double_cv (xb: q28_YY q28_NN q28_YN q28_NY = q28_dp > q28_p_high) (bid: q28bidca1000 q28bidY1000 q28bidN1000 = ) > ml search > ml maximize > > ********** > > Based on the model above one can then estimate mean and median WTP. As > an alternative to the model above, one can estiamte WTP directly. Let > exp(-zb) define the standard definition of the elements of the > log-likelihood, where z=[bid,x] refers to variables from my program > above, and b to the vector of parameters. Hence, this is what is > estimate above. To estimate WTP directly, the elements should instead be > exp((bid-xc)/d) where c are my new parameters of interest for my > covariates and d is a constant to be estimated. > > I have tried to estimate my model above by replacing ($ML_y6*`bid'+`xb') > with ((`bid'+`xb'/$c)) but I get the error message "Unknown function (), > r(133);". One way to obtain by c-vector is to estimate my model above > and to calculate c=b/$ML_yi ($ML_yi produces a single parameter for > `bid'). However, that means that I have to recalcualte all coefficient > estiamtes. My question is therefore, is it possible to specify my > log-likelihood to get b and c directly. > > Thanks > > Henrik Henrick, for the model outlined above, would your ultimate goal be to calculate mean and/or median WTP and eventually Krinsky and Robb confidence interval If so, can you send me the data for those variables in the model? The data would be for me to double-check my code. -- P. Wilner Jeanty, Post-doctoral researcher Dept. of Agricultural, Environmental, and Development Economics The Ohio State University 2120 Fyffe Road Columbus, Ohio 43210 (614) 292-6382 (Office) * * For searches and help try: * http://www.stata.com/support/faqs/res/findit.html * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

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