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Hi,

Suppose we have a design as below:

Design
;alts = alt1, alt2
;rows = 16
;eff = (mnl, d)
;block = 2
;model:
U(alt1) = b1*A[0,1,2,3,4,5,6,7] + b2.dummy[0|0|0]*B[0,1,2,3] + b3.dummy[0|0|0]*C[0,1,2,3] + b4*A*A/
U(alt2) = b1*A + b2*B + b3*C + b4*A*A
$

You can see that the design allows us to ...

Hi Andrew many thanks for your reply!

Thanks Michiel. I followed your suggestion and used the actual attribute levels in my code but found something strange when I included interaction terms:

When the levels are greater than one, adding interactions would work, e.g.,

Design
;alts = alt1, alt2
;rows = 16
;eff = (mnl,d)
;block = 2 ...

Thanks Michiel!

I have a quite silly question but I have been quite confused about what is the correct way to specify the attribute levels in Ngene.

Suppose I have an attribute 'cost' which has four levels: 10, 50, 100, 200

In terms of dummy coding, shall I specify it this way:

(A)
Design
;alts ...

Many thanks John and Michiel. Your suggestions are very helpful.

If I want to enter all attributes in the utility function using their log form (i.e., to specify a multiplicative utility function), how do I write the code?

Many thanks!

Dear Michiel

I generated an efficient design using dummy coding for all attributes; see below:

Design
;alts = alt1, alt2
;rows = 16
;eff = (mnl, d)
;block = 2
;model:
U(alt1) = b1.dummy[0|0|0|0|0|0|0]*A[0,1,2,3,4,5,6,7] + b2.dummy[0|0|0]*B[0,1,2,3] + b3.dummy[0|0|0]*C[0,1,2,3]/
U(alt2) = b1*A + b2 ...

My pleasure Michiel. I have been playing with different designs using Ngene today and found the orthogonal design always led to multiple solutions, i.e., for the same code using othorgonal design, each time I pressed the 'run' button I got different designs. Is this expected?

Then I am thinking if ...

Many thanks Michiel. I agree that the foldover design won't allow me to estimate so many dummy coded interactions and to estimate them will also need a very large sample size. I am quite new to design and just started to understand the differences between all these designs. I learned a lot from your ...

Hi Michiel

Many thanks for the prompt reply.

Efficient design was my first choice as there are a lot of constraints to impose (orthogonal design cannot impose constraints). However, our research team has decided to use dummy coding for all attributes and estimate the effects of several two way ...

Dear Michiel and John

Many thanks for your responses so far. They have been extremely helpful.

I wanted to run a sequential design with some two way interactions. Below is my syntax:

design
;alts = alt1, alt2
;rows = 16
;orth = seq
;block=2
;model:
U(alt1) = b1*A[0,1,2,3,4,5,6,7] + b2*B[0,1,2,3 ...