  The field of in-vivo neurophysiology currently uses statistical standards
that are based on tradition rather than formal analysis. Typically, data from
two (or few) animals are pooled for one statistical test, or a significant test
in a first animal is replicated in one (or few) further animals. The use of
more than one animal is widely believed to allow an inference on the
population. Here, we explain that a useful inference on the population would
require larger numbers and a different statistical approach. The field should
consider to perform studies at that standard, potentially through coordinated
multi-center efforts, for selected questions of exceptional importance. Yet,
for many questions, this is ethically and/or economically not justifiable. We
explain why in those studies with two (or few) animals, any useful inference is
limited to the sample of investigated animals, irrespective of whether it is
based on few animals, two animals or a single animal.
