Pilot DCE Design: Weak vs Strong Bayesian Priors?

[sara38]

Hello,

I am currently designing a discrete choice experiment to assess farmers’ willingness to reduce antibiotic use. My design is unlabelled, with two alternatives (A and B). I am trying to design a pilot study that will be delivered to 20 farmers to generate priors for designing the full survey.

I have 5 attributes that were developed following focus group discussions.
Health: supplement feed with minerals / supplement feed with vitamin C / no supplementation
Prevention: vaccinate / do not vaccinate
Treatment: use antibiotics / do not use antibiotics
Management: disinfect material / reduce animal density / increase ventilation / no management
Cost: 100 / 200 / 400 / 700

When I use weak/non-informative Beyesian priors in ngene (roughly 0.01–0.2 to reflect genuine uncertainty), the resulting designs perform poorly (S-estimates: 3626; Sp estimates: 0.4-3442; sp t-ratios: 0.03-2). To obtain designs with acceptable performance (S-estimates = 2.4; Sp estimate: 0.6-2.0; sp t-ratios: 1.4-2.4), I need to impose much stronger priors (around 0.4–0.6), which feels difficult to justify given the lack of evidence.

My question is:
For a pilot DCE with very limited prior information, is it generally preferable to use weak/non-informative priors and accept poorer design efficiency in order to reflect true uncertainty, then estimate priors for the main study; or impose stronger assumed priors in order to obtain a more statistically efficient and robust pilot design?
I do not want to design a "poor" experiment and be unable to extract any useful information from the pilot's data to design the full survey. On the other hand, I don't want to use priors that are too strong, as I genuinely do not have any information regarding preferences.

Any advice or practical experience with similar situations would be greatly appreciated!!

Many thanks,
Sara

PS: I even tried to run a much simpler design that removed the management attribute (which has 4 categorical variables), but I have the same problems for non-informative priors.
PS2: Unfortunately, I cannot get any information to help refining the priors before the pilot survey.