I am trying to estimate a travel cost model for whitewater recreation using
the usual negative binomial distribution. My sample is from an on-site survey
so I need to take into account the fact that my observations are truncated at
positive trip demand as people who have not visited the river are not included
and also the problem of endogenous stratification (the likelihood of being
sampled depends on the frequency of visiting the site).
my question is how I might take these 2 factors into account using the nbreg
function (negative binomial distribution)within Stata? Is there some optional
command that I can use along with nbreg?
Thanks for the help,
Stephen
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