Dear R experts,

I have conducted a power calculation in order to estimate the number of
subjects needed to detect an effect size of d=0.28 (cohen's d) for a
difference between two independent groups (alpha level should be 0.05 and
the effect should be detected with 80% probability).
The results from the code below indicates that I would need n=400 subjects
(200 in each group). This is seems so incredibly high that I mistrust my
results & wanted to ask whether I miscalculated n?

library(pwr)
pwr.t.test(d=0.28,sig.level=0.05,power=0.8,type="two.sample",alternative="two.sided")

Many thanks for you help!
Jokel

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