Allocation concealment as a potentially useful aspect of randomised experiments

In experiments where subjects are allocated to different treatments, implementing allocation concealment simply means that procedures are used to prevent conscious or unconscious human bias influencing the allocation of particular subjects to particular treatments. It is a related, but distinct, procedure to blinding. Allocation concealment is a neglected, but potentially valuable, tool in improving the design of experiments, and it can always be applied inexpensively and easily to any experiment involving allocation of subjects between treatment groups. I feel allocation concealment should be adopted more widely.

Significance statement

Allocation concealment simply means that the allocation of particular subjects to particular treatment groups in an experiment is not known to anyone prior to subjects being allocated to particular groups. It is a related but distinct procedure to blinding. Allocation concealment is a neglected but valuable tool in avoiding the introduction of biases into an experiment; and it can always be applied cheaply and easily. BES is right to encourage greater consideration of blinding, but it should also encourage allocation concealment.