Modification of the sample size and the schedule of interim analyses in survival trials based on data inspections, by H. Schäfer and H.-H. Müller, Statistics in Medicine 2001; 20: 3741-3751.

@article{Bauer2004ModificationOT,
  title={Modification of the sample size and the schedule of interim analyses in survival trials based on data inspections, by H. Sch{\"a}fer and H.-H. M{\"u}ller, Statistics in Medicine 2001; 20: 3741-3751.},
  author={Peter Bauer and Martin Posch},
  journal={Statistics in medicine},
  year={2004},
  volume={23 8},
  pages={1333-4; author reply 1334-5}
}