Most medical trials are monitored for early evidence of treatment differences or harmful side effects. In this paper we review and critique various statistical approaches that have been proposed for the design and analysis of sequential experiments in medical applications. We discuss group sequential tests, stochastic curtailment, repeated confidence intervals, and Bayesian procedures. The role that a statistical stopping rule should play in the final analysis is examined.
"Statistical Approaches to Interim Monitoring of Medical Trials: A Review and Commentary." Statist. Sci. 5 (3) 299 - 317, August, 1990. https://doi.org/10.1214/ss/1177012099