# st: Re: WTP from double bounded data

 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