Can I say "A test comprises an equal number of items concerned with either prospective or retrospective, long-term or short-term, and self-cued or environmentally-cued memory subscales"?
Judging from the context of options presented, I think you could slightly improve the clarity of what is meant in this sentence by inserting additional copies of "either":
A test comprises an equal number of items concerned with either prospective or retrospective, either long-term or short-term, and either self-cued or environmentally-cued memory subscales.
But I think a much better option than trying to load more into that sentence is to lay out the options in several sentences or a bullet list. For example, if I understand correctly:
A test comprises items concerned with various characteristics of memory subscales. These items should be equally split across:
- prospective and retrospective
- long-term and short-term
- self-cued and environmentally-cued
I think your statement is technically wrong. It can be written generally like this:
A Test comprises (something) with Either B1 or B2, C1 or C2 and D1 or D2
Which I interpret to mean that the test comprises something with:
- options from B and D, OR
- options from C and D
But not with options from B, C and D which is what I think you mean.
It might be more clear if you could say:
A test comprises (something) with one of each of the following options/parameters: (B1 or B2), (C1 or C2) and (D1 or D2).
A test comprises (something) with one of each of the following options/parameters:
- B1 or B2
- C1 or C2
- D1 or D2