@misc{indiciae1cfe97057803,
  title = {Interim analysis: the alpha spending function approach.},
  author = {D L DeMets and K K Lan},
  doi = {10.1002/sim.4780131308},
  url = {https://pubmed.ncbi.nlm.nih.gov/7973215/},
  note = {Source identifier: 7973215}
}