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I'm on the stage of experiment design of some biomedical time-course study. Let's say we will have 2 groups of subjects - case and control. The total number of subjects is limited (for example, 30), and we need to decide how it's better to split subjects between case and control. One way is to have balanced dataset 50% of case vs. 50% of control. Another way is to assign 2/3 of subjects to case and 1/3 to control, since the case subjects would be more interesting.

What experiemnt design would you suggest? Which issues/pitfalls should be considered in both case? Should the experiment design depend on questions asked?

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Are you assigning patients to cases or control, or merely collecting those who happen to be cases and controls? – EpiGrad Nov 28 '12 at 2:42
@EpiGrad: Yes, we're assigning. But did I say patients? The question is more general. Subjects can be mice, for examples. Are you thinking about any ethical issues with humans? – yuk Nov 28 '12 at 20:55
No, but I tend to read "biomedical" and head straight toward human subject. That's my own bias :) – EpiGrad Nov 28 '12 at 20:58

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Even if the case subjects are more interesting, I would recommend using balanced group sizes. Reason: AN(C)OVA and other analysis methods are more robust when group sizes are equal. See, e.g., Glass, Peckham and Sanders (1972).

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Stephan, thanks for your input. – yuk Nov 28 '12 at 20:53

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