After inserting priors,MNL model failing to converge

This forum is for posts that specifically focus on Ngene.

Moderators: Andrew Collins, Michiel Bliemer, johnr

After inserting priors,MNL model failing to converge

Postby JasonOng » Thu Nov 29, 2018 9:29 pm

Dear NGENE team

After collecting information from my pilot, I tried inserting priors into my D-efficient MNL design but NGENE seems to be having trouble finding a design
I included coefficients that were statistically significant and left the rest as 0
what do you suggest I do?
thanks for your help

Kind regards,
Jason Ong

Code: Select all
Design
; alts = A*, B*, C
; rows = 24
; eff = (mnl,d) 
?; bdraws = gauss(5)
; block =2
; con
; model:
U(A) = b1.effects[0|0|-0.9]*Cost[500,1000,2000,0] +
       b2.effects[0|0|0|-1|0|0|0]*Loc[1,2,3,4,5,6,7,0] +
       b3.effects[0|0]*Test[1,2,0] +
       b4.effects[0|0|0]*Person[1,2,3,0] +
       b5.effects[0]*Access[1,0]/
U(B) = b1*Cost +
       b2.effects*Loc +
       b3.effects*Test +
       b4.effects*Person +
       b5.effects*Access/
U(C) = b6[-1.4]
$
JasonOng
 
Posts: 4
Joined: Mon Oct 29, 2018 12:50 am

Re: After inserting priors,MNL model failing to converge

Postby Michiel Bliemer » Sat Dec 01, 2018 9:29 am

Checking for dominance (you added a * to alts A and B) with mostly zero priors is problematic since every choice task will have a dominant alternative. You either need to remove the asterisks or you need to insert non-zero priors.

Instead of using zeros for non-significant priors, you can use normally distributed Bayesian priors where the parameter estimate is used as the mean and the standard error is used as the standard deviation. Note that you have a lot of priors so you will need to assume some priors to be fixed instead of random. Using gauss(5) will do millions of draws if you use a lot of Bayesian priors, so you may need to reduce this to gauss(2) or gauss(3).

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


Return to Choice experiments - Ngene

Who is online

Users browsing this forum: dtobin02 and 10 guests

cron