[Limdep Nlogit List] Status quo/ no-choice option SP data set-up

[Paraic Carroll]

Hi there,

I am conducting a SP mode choice experiment in which there are 3 modes/
alternatives (car, walk, cycle). Walk and cycle have three attributes with
3 levels each (infrastructure, time and adjacent traffic speed) that are
improved to various degrees by a range of policy measures in the scenarios.
However, car is being treated as a 'status quo' option that has no
attributes associated with it.

I have run a couple basic MNL models that have produced poor outputs in
terms of high p-values and coefficients that are not significant which
seems to suggest that maybe I have the dataset coded wrong.

I have been following the Shoe Brand Choice example conducted by William
Greene and I have tried to set the data up in the same way (e.g. fashion,
quality, price, asc4). However as my attributes are on three levels and not
two like the fashion and quality attributes I am unsure how to code them,
also in the shown dataset for this experiment price is coded 0.12, 0.08,
0.2 etc. and not 1,2,3,4 which confused me.

I have tried design coding (1,2,3), effects coding (-1,0,1) as well as
using the numerical values from the survey for the 3 attiribute levels in
each attribute, leaving the car option with a 0 constant and I have created
an ASC variable with 1 = car 'status quo' and 0 = other alternatives.

I am wondering if I am doing the right thing here or if I have made an
error in how I have prepared the data. I am also thinking that maybe a
nested model would be more suited to what I am trying to model.

Any suggestions would be greatly appreciated,

Kind regards,

Páraic