The goal is to reach a conclusion about the treatment value as soon as possible, to avoid subjecting patients to inferior treatments. However, repeatedly checking the results will increase the probability of Type-1 error. In such circumstances, akin to multiple testing, the overall alpha must be adjusted and shared among the various looks.
Word #35 – Interim Monitoring
In the interim monitoring of clinical trials, multiple looks are taken at the accruing patient results - say, response to a medication.