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From |
"Henrik Andersson" <[email protected]> |

To |
<[email protected]> |

Subject |
st: WTP from double bounded data |

Date |
Wed, 30 Jan 2008 21:36:47 +0100 |

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 * * 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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