Bioequivalence and Bioavailability Forum

Dear all,

I am trying to spell out the underlying model of FDA's pop BE analysis used for in vitro comparison of signle actuator content and more. A link is here.

The players are:

The formulations (F, two levels)
The stages (S, three levels in FDA's example, but may be anything from one upwards)
The cans ("Cans in batch", C, at least ten levels)
The batches ("batch within formulation", B, at least three levels)

I was initially thinking
Y=F+S+C+B+e_k where e_k is N(0, MSW_k), and where Y is the in vitro metric we are sampling, like SAC, and where we's consider C, possibly B and S random (?).

But since MSW_k comes from sampling across stages, I am inclined to work without S, so
a. Y=F+C+B+e_k,
where C and possibly B are random. When there is only a single sampled stage I guess this would then be
b. Y=F+B+e_k where e_k is then N(0, MSB_k)

What's your opinion on a. and b.?
How would you formulate the models yourself?