There are many software available for constructing a Simon's design. These software usually give sample sizes and critical values for stages 1 and 2, therefore, hypothesis testing is simple to conduct. Analyzing the data beyond hypothesis testing, however, is not straightforward when a Simon's design is used. When the actual stage 2 sample size is different from the one originally planned, data analysis is even more complicated. Many previously published clinical trials do not correctly account for such mid-course changes.
We present a simple R function for inference from Simon's two stage design: twostage2020Web.R The method is based on "Proper inference from Simon's two-stage designs" by Koyama and Chen (Statistics in Medicine [2008]).