[Limdep Nlogit List] Is a multinomial logit model with selection applicable here?

[William Greene]

James.  Selection into the estimation sample is not supposed to be one of
the choices.  Your
choice set should not include "no trip."  On the other hand, if you want to
include NO TRIP
as one of the choices, then I suspect you should not be using the selection
model.  This is not
well defined for the selection model.  In theory, the selectivity treatment
is trying to isolate the
difference in trip choices between those "selected" and those "not
selected."  But, none of
your non-selected observations made a trip, so the comparison is not
possible.
/B. Greene

On Tue, Feb 15, 2022 at 4:21 PM James Giller via Limdep <
limdep at mailman.sydney.edu.au> wrote:

> Hi,
>
> My dependent variable is based on travel mode choice survey data, and it
> has a value for "make no trip at all" as well as values for various modes,
> car, transit, taxi, walking, etc. The mode is only observed if the survey
> participant would make a trip, which made me consider a sample selection
> model.
>
> My dependent variable Y has the following values:
> 0 = transit
> 1 = car
> 2 = carpool
> 3 = taxi
> 4 = walking
> 5 = other
> 6 = no trip
>
> I created another variable DOTRIP, which is 0 if Y = 6, and 1 otherwise.
>
> I then tried to estimate the following model
> PROBIT ; Lhs = DOTRIP ; Rhs = <explanators> ; Hold $
> MLOGIT ; Lhs = Y ; Rhs = <explanators> ; Selection ; Pts = 25; Halton $
>
> The above model on the data set as explained returned an error message that
> there is insufficient variation in the dependent variable during the MLOGIT
> part. I think this is because the value 6 (no trip) is possible for Y, but
> none of the observations would be selected in the selection step.
>
> Am I correct in specifying a model with sample selection in this case? Or
> should I take a different approach to account for the individuals first
> deciding whether or not to travel, then by which mode?
>
> Is there some way to rearrange my data so that the above model will work?
>
> Thank you.
> James.
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>

-- 
William Greene
Department of Economics, emeritus
Stern School of Business, New York University
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