Dear all,
I need to calculate the sample size for a non-inferiority trial (normal
data).
I have an issue with the choice of alpha in the sample size calculation
formula. I am not sure if I need to set my type error I (alpha) at half the
conventional type I error used in two-sided confidence intervals.
Unfortunately, I don’t have access to any sample size calculations book that
deals with non-inferiority/equivalence issues.
Searching in the Internet I found various examples where some calculate the
sample size setting alpha to be 0.05 and some setting alpha to be 0.025.
I know that for the analysis I need to either calculate a two-sided 95%
confidence interval (equal-tailed) and then use the lower bound for testing
the hypothesis or calculate one-sided intervals with a coverage probability
of 97.5%. My issue is if in the sample size calculation I set alpha as 0.05
or 0.025.
Any help would be appreciated,
Ioanna
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