  In a group sequential clinical trial, accumulated data are analysed at
numerous time-points in order to allow early decisions about a hypothesis of
interest. These designs have historically been recommended for their ethical,
administrative and economic benefits. In this work, we discuss a collection of
new Stata commands for computing the stopping boundaries and required group
size of various classical group sequential designs, assuming a normally
distributed outcome variable. Following this, we demonstrate how the
performance of several designs can be compared graphically.
