Specifying Random Block factor in classic DOE designs

[#1]

Hi all,

When generating a classic DOE design in JMP, any block factor is automatically defaulted as fixed block factor. I know I can change it to random block effect to utilize the REML method by adding to it the "random effect" attribute in the Fit Model platform. However, I notice that I could also change its design role to "Random block", it is not automatically assigned the "random effect" attribute in Fit Model. So is there any difference between "Blocking" and "Random block" as design role options? The only thing I've noticed is that the block factor is shown in the Prediction Profiler when it's assigned "Random block" but not when it's "Blocking". Also, Fit Definitive Screening platform only works with "Blocking" but not "Random block" design role.

Thank you.

[#2]

My point about the restriction against random effects pertains to the use the special fitting process that Brad created for DSD. Of course, you may use any analysis method with the DSD.

Two blocks will yield very little information about the random effect. The estimate of the variance will be poor. On the other hand, the ability to assign any variation to the block will improve the estimation of the fixed effects.

Do you have prior experience with a 'day' effect?

[#3]

@statman and @Mark_Bailey, thank you both the helpful discussions. These are great points for me to keep in mind as I go about planning my experiments.