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different coeffients for one attribut

PostPosted: Tue Nov 04, 2014 4:32 pm
by mdann
hello everyone,

to create an efficient design I create a pretest with an orthogonal design within the attribut alt= b1+ b1*A[1,2,3,4]+ b2 * B[....].... where the levels stand for ordinal aspekts. 1 means ripping, 2 half ripping, 3 litter, 4 rubber mat (I dont`t know if eine use the right translation, but the content is important).

To create a mixlogit model I coded this attribut to dummy variables. As results I got for each level one a b-coefficient and the standard deviation. e.g.:

means rippimg: b=-0,8, std=0,2
half ripping: b=-0,3, std=0,15
litter: b=0,4, std= 0,1
rubber mat: b=0,2, std=0,3

Q1: Means that for creating an efficient design, that each level has to be transformed to a new dummy coded attribut like: ??

...b1[n,-0,8,0,2] * A[0,1] + b2[n,-0.3, 0.15] * B[0,1]..

Q2: Or is there a possibility to put all coefficients together so that I have already one attribut as before???

Q3: I saw in some syntaxes a vertical bar. What does this mean?

Thank you in advance!!

Re: different coeffients for one attribut

PostPosted: Tue Nov 04, 2014 5:50 pm
by Michiel Bliemer
The syntax b1.dummy[x|y|z] * A[1,2,3,4] means that A = 4 is the reference level (with a zero utility attached), A = 1 has a utility (coefficient) of x attached, A = 2 has a utility (coefficient) of y attached, and A = 3 has a utility (coefficient) of z attached.

In your case, your mixed logit model would be something like:

b1.dummy[n,0.8,0.2|n,-0.3,0.15|n,0.4,0.1] * A[1,2,3,4]

Note that the number of coefficients (3) is always one less the number of attribute levels (4), because the last level is the reference level. Therefore, I do not understand your estimation results, because one of the attribute levels should have a zero coefficient as the reference level. So which attribute level did you use as reference?

Michiel

Re: different coeffients for one attribut

PostPosted: Tue Nov 04, 2014 6:40 pm
by mdann
Hey Michiel,

thank you a lot!

I got 4 coefficients by changing the basic in a second process.

Micha

Re: different coeffients for one attribut

PostPosted: Wed Nov 05, 2014 8:02 am
by Michiel Bliemer
It does not make sense to change the reference level and obtain the final coefficient, as changing the reference level will impact upon all parameter estimates. You have to select a single reference level and stick with it, and only estimate 3 coefficients, you cannot estimate 4 coefficients. You can use effects coding or orthonormal coding instead of dummy coding if you wish.