Allocation Concealment

What It Is

In randomized trials, this is preventing people involved in conducting the trial from knowing the sequence of treatment assignments produced by randomization. In other words, when a participant is enrolled it is not known what treatment they will be assigned to.

Why It’s Important

When investigators and others know the randomization schedule (sequence of treatment assignments), they can subvert the process and negate the benefits of randomization. They can select which patients get into a particular study group, essentially “unrandomizing” the trial and causing groups not to be equivalent on important characteristics. There are documented instances of this.