01-03-2017 05:48 PM
I need to calculate the sample size in person-years for a single group prospective cohort study (surveillence study) aiming to demonstrate non-inferiority. I have some information based on population A from a previous study. I want to obtain the sample size needed to show that the events of interest in population B is non-inferior to population A by some margin or error. In SAS, there is a one-sample one-sided method for analyzing proportions. However, my event is extremely rare. Through quite a bit of searching it seems that the normal approximation is being used to calculate sample sizes such as in my case. At this point, I have decided to use PROC POWER’s non-inferiority test for a proportion. Does anyone know if it is acceptable by the FDA (or the standard) to use the normal approximation assumption to calculate sample size for non-inferiority trials even when the event is rare? If it is not acceptable, does someone have advice on which method/procedure you might use or have used? Or to the software that may help?