Hi,
We are planning to conduct an RCT comparing nitroglycerine patches to decrease the failure rates of radial arterial cannulation. Based on our audit, we expect a 30% failure rate in the placebo arm. We hypothesize that the NTG patch applied for 30 or 45 minutes could reduce the incidence of failure rate by 30%, which corresponds to a 9% absolute risk difference. We want to assume a type I error of 5% and aim for a power of 80%. How much sample size is needed per group?
Since there are three independent groups (placebo, NTG for 30 minutes, NTG for 45 minutes), I am unable to calculate it on Stata.