@misc{indiciae674af6af6b51,
  title = {Four problems with group sequential methods.},
  author = {J Whitehead},
  year = {1991},
  doi = {10.1016/0197-2456(91)90029-l},
  url = {https://pubmed.ncbi.nlm.nih.gov/1645644/},
  note = {Source identifier: 1645644}
}