wpgsd 
Weighted parametric group sequential design (WPGSD) allows one to take advantage of the known correlation structure in constructing efficacy bounds to control family-wise error rate (FWER) for a group sequential design. Here correlation may be due to common observations in nested populations, due to common observations in overlapping populations, or due to common observations in the control arm.
Installation
Install the development version of wpgsd from GitHub:
remotes::install_github("Merck/wpgsd")References
Anderson, K. M., Guo, Z., Zhao, J., & Sun, L. Z. (2022). A unified framework for weighted parametric group sequential design. Biometrical Journal, 64(7), 1219--1239.
BibTeX entry:
@article{anderson2022unified,
title = {A unified framework for weighted parametric group sequential design},
author = {Anderson, Keaven M and Guo, Zifang and Zhao, Jing and Sun, Linda Z},
journal = {Biometrical Journal},
volume = {64},
number = {7},
pages = {1219--1239},
year = {2022},
publisher = {Wiley Online Library}
}