Dear Ngene team,

I am currently working on a new consumer survey that will include a CE. I would like to use a Bayesian design.

As a first step, following the indications in the manual and those that I found in this forum I run a d-efficient design based on a mnl model, setting all priors equal to zero. This is because I cannot really guess about the direction of the attribute levels, except for price which is expected to be negative. Using the sintax below I obtained a d-error equal to 0.345, which I suppose (please correct me if I am wrong!) may be good enough for a pilot survey.

Design

;alts = alt1, alt2, alt3

;rows = 28

;block = 4

;eff = (mnl,d)

;model:

U(alt1)= b1[0]*price[0.33, 0.39, 0.45, 0.51, 0.57, 0.63, 0.69] + b2.dummy[0|0|0]*Plastic[0,1,2,3] + b3[0]*Colour[0,1]/

U(alt2)= b1*Price + b2.dummy*Plastic + b3*Colour

$

However, I was wondering whether, in this phase, it would be better to use uninformed Bayesian priors with uniform distribution e.g., [(u, 0, 1)] (assuming that attribute levels would have the same impact on the utility) instead of setting priors equal to zero.

Furthermore, since I cannot refer to the S-estimate how can I establish the proper number of respondents for the pilot test in order to obtain reliable priors for the final Bayesian design?

I apologize in advance if these issues have already been asked before.

Thank you very much for your help.

Eli