I would like to calculate a sample size for 3 groups based on the mean for each of the three groups of an continuous variable (Flow per min). Its a randomised study with an allocation ratio of 1:1:1. From the litterateur i know the following means: Group1 =30, group2 =39, group3= 35 I would like the significance level = 0.05 and set the power to 0.80.
So far i tried to use the pwr package, and i end up with a sample size of 52 for each group.
But here i just use the cohen recommend middel effect sixe F= 0.25 and i would rather that the calculation was based on the means from the literature.
All help very much appreciated.
´´´´ pwr.anova.test(k=3,f=.25,sig.level=.05,power=.8) ´´´´