[Limdep Nlogit List] Nlogit4 and bimodal distributions

[Leif]

Stephen,
Look into using a latent class logit with 2 classes.  That will resemble 
the distribution you're talking about.  You could even constrain all 
parameters except the limit to be the same for the 2 classes - just 
allowing for 2 sets of preferences on the limit variable.

You might also want to redefine the limit as dummy variables because (as 
you mention) catch and release is likely very different than keeping any 
fish and might need to be modeled as such.

Leif
leifand at u.washington.edu



On Thu, 1 Nov 2007, Stephen Beville wrote:

> I'm a new-comer to choice modelling and I'm investigating anglers'
> recreational fishing site choices using  Nlogit4.0 and stated preference
> data. I'm having trouble getting a good fit, or in other words significant
> t-stats, for the attribute in the model, "bag limit" (i.e. # of fish anglers
> can take home) which in my design has been specified with levels (0,2,4).
> The attribute is insignificant with an MNL specification and also when I try
> a random parameter specification using normal, uniform, triangular
> distributions. I've also tried constraining the variances of the
> distributions to (to allow for a wide variance), and still have not achieved
> a desired fit-though the fit improved over the MNL model usign a triangular
> distribution constrained so that the variance was eqaul to twice the mean.
>
> The underlying problem I believe, as to why the parameter is insignificant
> in all mentioned cases, is due to extreme heterogeneity in angler
> preferences, or preference poles.   Where a large portion of the angler
> respondents view (prefer) the attribute level (0), or in other words catch
> and release, because it may in their minds represent a proxy for high
> fishing quality and where some anglers view the attribute level (4) as
> preferable because they can take more fish home.
>
> Hence, I believe what I really need to use is a bimodal distribution which
> has two peaks-one for catch and release-oriented anglers and one for
> consumption-oriented anglers. Can anyone please advise me if Nlogit is
> capable of specifying a bimodal distribution or bimodal-like distribution.
> Or offer any suggestions how I may solve this conundrum.
>
> Thank you so much for any help you can offer.
>
>
> -- 
> Stephen Beville
> PhD Candidate ESD
> Lincoln University
> (027) 338 8438
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