To cite package ‘gsDesign2’ in publications use:

  Anderson K, Zhao Y, Zhang Y, Blischak J, Xie Y, Xiao N, Yang J
  (2026). _gsDesign2: Group Sequential Design with Non-Constant
  Effect_. R package version 1.1.9,
  <https://CRAN.R-project.org/package=gsDesign2>.

A BibTeX entry for LaTeX users is

  @Manual{,
    title = {gsDesign2: Group Sequential Design with Non-Constant Effect},
    author = {Keaven Anderson and Yujie Zhao and Yilong Zhang and John Blischak and Yihui Xie and Nan Xiao and Jianxiao Yang},
    year = {2026},
    note = {R package version 1.1.9},
    url = {https://CRAN.R-project.org/package=gsDesign2},
  }