Two attributes that are completely dependent -- constraint?

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Two attributes that are completely dependent -- constraint?

Postby tanner1 » Thu Aug 22, 2019 4:23 am

Hi all,

I am a very new user of Ngene and choice experiment design generally. When you need one attribute completely dependent on another, should it be introduced as a constraint, or do you simply make a design with one fewer attributes?

Example code is below for a design with:
- 3 2-level variables (qualitative), 2 of which are completely dependent on each other
- 1 4-level quantitative variable
- an opt-out alternative (alt3):

Code: Select all

Design
;alts = alt1, alt2, atl3
;rows=12
;block=4
;eff=(mnl,d)

;cond:
if(alt1.project=1, alt1.location=1),
if(alt1.project=2, alt1.location=2),
if(alt2.project=1, alt2.location=1),
if(alt2.project=2, alt2.location=2),

;model:
U(alt1)=cost[0]*cost[1,3,7,10]+project.dummy[0]*project[1,2]+location.dummy[0]*location[1,2]+type.dummy*type[1,2]
U(alt2)=cost[0]*cost[1,3,7,10]+project.dummy[0]*project[1,2]+location.dummy[0]*location[1,2]+type.dummy*type[1,2]
U(alt3)=asc
$


This code produces MNL D-errors of >1500 and I'm also not sure if that is a concern or not.
tanner1
 
Posts: 6
Joined: Tue Jun 25, 2019 8:28 am

Re: Two attributes that are completely dependent -- constrai

Postby Michiel Bliemer » Thu Aug 22, 2019 10:18 am

Yes those high D-errors are an indication that the model is not identifiable. I have responded more extensively to your other post in the SCE forum.

Michiel
Michiel Bliemer
 
Posts: 1705
Joined: Tue Mar 31, 2009 4:13 pm


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