study design group sequential design Philippe Rocca-Serra adapted from https://www.jstatsoft.org/article/view/v066i02/v66i02.pdf group sequential design is a study design used in clinical trial settings in which interim analyses of the data are conducted after groups of patients are recruited. After each interim analysis, the trial may stop early if the evidence so far shows the new treatment is particularly effective or ineffective. Such designs are ethical and cost-effective, and so are of great interest in practice. https://cran.r-project.org/web/packages/gsDesign/index.html ready for release