Approaches to Selecting "Time Zero" in External Control Arms with Multiple Potential Entry Points: A Simulation Study of 8 Approaches.

There are multiple methods available from which an analyst may select "time zero" in an external control cohort.This simulation study demonstrates that some methods perform poorly but most are viable options, depending on context and the degree of overlap in time zero across cohorts.Careful thought and clear justification should be used when selecting the strategy for a study.