Group Sequential Testing of a Treatment Effect Using a Surrogate Marker R package SurrogateSeq version 1.1 CRAN Task View: ClinicalTrials (https://CRAN.R-project.org/view=ClinicalTrials) 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) <doi:10.1093/biomtc/ujae108>. 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/>. Software Depends: R (>= 3.5.0) Imports: stats, MASS, ggplot2 Layla Parast <parast@austin.utexas.edu> Comprehensive R Archive Network (CRAN) Layla Parast [aut, cre], Jay Bartroff [aut] GPL 2026-01-08 application/tgz https://CRAN.R-project.org/package=SurrogateSeq doi:10.32614/CRAN.package.SurrogateSeq