I have two questions :
I am wondering if it is possible to know the size of the sample (n) for a multiple linear regression if I want the tests to be powerful enough ? To me, it seems very difficult in reality to use the calculation of power for the multiple linear model, because it would be necessary to enter valid values for the different parameters. Is it possible to do that with R ? If yes, How can I do this with R ? The R code ?
With R, there is this code for the multiple linear regression :
pwr.f2.test(u = NULL, v = NULL, f2 = NULL, sig.level = 0.05, power = NULL)
u : degrees of freedom for numerator
v : degrees of freedom for denominator
f2 : effect size
sig.level : Signiﬁcance level (Type I error probability)
power : Power of test (1 minus Type II error probability)
- Is it possible to improve this R code to take account of (consider) the size of the sample (n) and the different parameters of the regression ?
- What about the size of the sample (n) for a logistic regression (logit regression)? Is it possible to know the size of the sampling knowing some criterion like (sig.level=0.05, power=0.8…)?