Hi,
I would to maximize the likelihood function for interval data from a dichotomous stated preference study. In this kind of study respondents are first asked if they are accepting to pay a certain bid (bid0). Depending on their answer they are then asked whether they accept a second higher bid (bid1) if they answered yes to the first question and a second lower bid if they answered no (bid 2).
My log likelihood is made up of four parts and is given by
LL=-{
YY*ln(1+exp(-($a+$c*bid1+`Xb')))
+NN*ln(exp(-($a+$c*bid2+`Xb')))/(1+exp(-($a+$c*bid2+`Xb')))
+YN*ln((exp(-($a+$c*bid1+`Xb')))/(1+exp(-($a+$c*bid1+`Xb')))-(exp(-($a+$c*bid0+`Xb')))/(1+exp(-($a+$c*bid0+`Xb'))))
+NY*ln((exp(-($a+$c*bid0+`Xb')))/(1+exp(-($a+$c*bid0+`Xb')))-(exp(-($a+$c*bid2+`Xb')))/(1+exp(-($a+$c*bid2+`Xb'))))}
where
YY = variable that defines respondent who has answered yes to initial and follow-up bid
NN = variable that defines respondent who has answered no to initial and follow-up bid
YN = variable that defines respondent who has answered yes to initial but no follow-up bid
NY = variable that defines respondent who has answered no to initial but yes follow-up bid
bid0=initial bid level
bid1= follow-up bid (2*bid0)
bid2= follow-up bid (bid0/2)
X = other covariates
a, b, and c = parameters
The variables YY, NN, YN, and NY can be defined as both dummies or a continuous variable. The intervals for the bid levels may overlap since the initial bid level is varied among respondents.
My experience from programming in Stata is very limited (close to nonexisting) so I don't know if what I want to do is trivial to solve, or if it is not possible to do. I would be very grateful for any help.
Thank you
Henrik
Corresponding address Sep 2007 until May 2008:
Henrik Andersson
Program in Health Decision Science
Harvard School of Public Health
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phone +1-617-432-0394
fax: +1-617-432-0190
email: [email protected]
www.healthdecisionscience.hsph.harvard.edu
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Henrik Andersson
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Dept. of Transport Economics
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