[Date Prev][Date Next][Thread Prev][Thread Next][Date index][Thread index]

st: WTP from double bounded data

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 $ML_y1 ==
	qui replace `lnf' = ln(invlogit(-($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 

** 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.



*   For searches and help try:

© Copyright 1996–2024 StataCorp LLC   |   Terms of use   |   Privacy   |   Contact us   |   What's new   |   Site index