Group Sequential Testing of a Treatment Effect Using a Surrogate Marker

Provides functions to implement group sequential procedures that allow for early stopping to declare efficacy using a surrogate marker and the possibility of futility stopping. More details are available in: Parast, L. and Bartroff, J (2024) . A tutorial for this package can be found at < https://www.laylaparast.com/surrogateseq>. A Shiny App implementing the methods can be found at < https://parastlab.shinyapps.io/SurrogateSeqApp/>.