[R] delta and sd parameters for power.t.test

Lasse Kliemann lasse at lassekliemann.de
Thu Dec 14 23:26:54 CET 2017

What is the rationale behind having both the delta and sd parameters for
the power.t.test function? For the relevant noncentrality parameter, we
only need the ratio delta/sd. If my effect size is given as Cohen's d,
then I only got that ratio and not sd.

As far as I see, in such a case, I can specify delta=d and leave sd at
its default value 1. Is this correct or am I missing something?

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