modelling error structure with a pilot study in pharmacology sounds funny,
specially with 6 mice in each group, Nick. Math and statistics sometimes
blind researchers.
I would not try to answer anything with a pilot study (in
pharmacology/biochemistry, etc..).
Pilots are done to see the direction of the effect. If it shows a signal,
we keep going. If not, we stop and try other alternatives. Mann-whitney
sounds ok, at least in my modest view.
Tiago
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