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Hello,

May I kindly ask you to elaborate on the potential reasons I get the "Error Undefined" result with the following syntax, even though my utility functions are not complicated and the prior parameters are non-zero?

Design
;alts = Alt1, Alt2
;rows = 180
;eff = (mnl, d)
;alg = mfederov(candidates = selection_1000_modification_2_comma_delimited.csv)
;block = 20
;model:
U(Alt1) = b1.dummy[0.2] * ToolSupply[0,1] +
b2.dummy[0.15] * Weather[0,1] +
b3.dummy[0.25|0.25] * Traffic[0,1,2] +
b4.dummy[0.2|0.2] * Insurance[0,1,2] +
b5.dummy[0.15] * Locker[0,1] +
b6.dummy[0.3|0.3|0.3|0.3] * WorkingHours[0,1,2,3,4] +
b7[0.1] * BikeLines[0:1] +
b8[0.25] * CompPerPackage[40:160] +
b9[0.2] * CompPerKM[20:60] /

U(Alt2) = b1 * ToolSupply +
b2 * Weather +
b3 * Traffic +
b4 * Insurance +
b5 * Locker +
b6 * WorkingHours +
b7 * BikeLines +
b8 * CompPerPackage +
b9 * CompPerKM $

Thank you.

1. Please write out your levels for the numerical attributes. Instead of CompPerPackage[40:160], which is not defined in Ngene, simply write something like CompPerPackage[40,60,80,100,120,140,160]. Ngene does know a shortcut, namely 40:160:20, where the last value is the step size. The syntax 40:160 can only be used in combination with another algorithm, which I would not recommend.

2. You may want to use ;alts = alt1*, alt2* to automatically avoid dominant alternatives, although this will not be a major issue in your script.

3. Your priors are somewhat problematic; a prior of 0.25 for CompPerPackage, where levels range from 40 to 160, is very large. Instead of choosing priors manually, they preferably come from a pilot study as it is very difficult to guess priors and choosing wrong priors can make the design very inefficient.

If you still receive an error message after fixing 1, then the issue is likely in your candidate set. Make sure that all levels in the candidate set also appear in the script.

Michiel

Thank you very much! I will fix the issues you mentioned. Although it may not be relevant to my previous question, may I ask how we add the "opt-out" to our final design? How should I arrange my script accordingly?

Beyza

For an opt-out you add a third alternative with only a constant:

U(optout) = b0[..]

Michiel