Interim monitoring of efficacy data is important and appropriate.

@article{Sydes2008InterimMO,
  title={Interim monitoring of efficacy data is important and appropriate.},
  author={Matthew R. Sydes and Mahesh K B Parmar},
  journal={Journal of clinical epidemiology},
  year={2008},
  volume={61 3},
  pages={203-4}
}