by johnr » Mon Sep 07, 2015 11:15 am
Hi Cristobal
Hensher et al. (2011) used data from an experiment I generated for consulting project. I generated the design for that project outside of Ngene as Ngene at the time could not handle the fact that the combination of the probability attributes had to sum to one. We have since implemented the ability to do this. Here is an example (from another project I worked on), where I have three attributes for Probability (CPr1, CPr2 and CPr3, each associated with different travel times (CTT1, CTT2, CTT3), similar to how the data was set up in the paper you cite. Here, the probabilities are interacted with the travel times. Note that the last probability CPr3, is a function of the probabilities for the first two attributes (1 - pr1 - pr2), hence, if Pr1 = 0.2 and Pr2 = 0.3, then Pr3 = 0.5...
... + Pr1TT1[-0.04] * CPr1[0.1,0.2,0.3,0.4] * CTT1[49,56,63]
+ Pr2TT2[-0.05] * CPr2[0.2,0.3,0.4,0.5] * CTT2[66.5,70,73.5]
+ Pr3TT3[-0.06] * CPr3[fcn(1 - Car.CPr1 - Car.CPr2)] * CTT3[77,84,91] ....
Other than that, the experiment you mention was actually a pivot design, hence the attributes were pivoted off of a respondent reported reference alternative. it was not generated specifically for the testing prospect theory (though given that it is based on a respondents reported reference alternative, it can test aspects of this theory (see Hess et al. 2008). This type of design is discussed in
Rose, J.M., Bliemer, M.C.J., Hensher, D.A. and Collins, A.T. (2008) Designing Efficient Stated Choice Experiments Involving Respondent Based Reference Alternatives, Transportation Research Part B, 42(4), 395-406.
Hess, S., Rose, J.M. and Hensher, D.A. (2008) Asymmetric Preference Formation in Willingness to Pay Estimates in Discrete Choice Models, Transportation Research Part E, 44(5), 847-863.
This type of design is also implemented in Ngene. So, in theory, if you combine the pivot design approach with the attribute function command shown above, Ngene should be able to generate a similar type of design to the original one.
John