Pilot testing using an D efficient design
Posted: Tue Feb 24, 2026 2:38 pm
Dear Michiel,
I am conducting an experimental design with 6 attributes (4 with three levels and 2 with four levels; two of them are numerical levels). I now have a few questions I would like to consult you about. Note: I used two check constraints, so the modified M algorithm was employed.
1. I want to set three options (i.e., alt1, alt2, none). When defining the utility function, U(alt1) = b1*B, U(alt2) = b2*B. Should U(none) be set to 0 or represented by b_optout? I tried setting U(none) = 0/b_optout separately and found that the D-values from the two results differ.
2. One attribute is a monetary incentive attribute. In the pilot study stage, would you recommend using [+] to indicate preference order? (Other attributes do not have a clear preference order.)
3. If I treat the monetary incentive attribute as a continuous variable and the time attribute as a dummy variable (e.g., 5, 10, 15 min), is this acceptable? Or would it be better to treat both as dummy variables?
4. If there are a total of 14 parameters, then S >=7. Does the "7" refer to the total number of choice sets being > 7, or does each version need to be > 7?
5. If the pilot study uses rows=12, block=2, while the formal study uses rows=24, block=4, is this feasible?
Thank you in advance for your patient response.
Nancy
I am conducting an experimental design with 6 attributes (4 with three levels and 2 with four levels; two of them are numerical levels). I now have a few questions I would like to consult you about. Note: I used two check constraints, so the modified M algorithm was employed.
1. I want to set three options (i.e., alt1, alt2, none). When defining the utility function, U(alt1) = b1*B, U(alt2) = b2*B. Should U(none) be set to 0 or represented by b_optout? I tried setting U(none) = 0/b_optout separately and found that the D-values from the two results differ.
2. One attribute is a monetary incentive attribute. In the pilot study stage, would you recommend using [+] to indicate preference order? (Other attributes do not have a clear preference order.)
3. If I treat the monetary incentive attribute as a continuous variable and the time attribute as a dummy variable (e.g., 5, 10, 15 min), is this acceptable? Or would it be better to treat both as dummy variables?
4. If there are a total of 14 parameters, then S >=7. Does the "7" refer to the total number of choice sets being > 7, or does each version need to be > 7?
5. If the pilot study uses rows=12, block=2, while the formal study uses rows=24, block=4, is this feasible?
Thank you in advance for your patient response.
Nancy