Article Text

Download PDFPDF

Assessing allocation concealment and blinding in randomised controlled trials: why bother?
  1. Kenneth F Schulz, PhD, MBA
  1. Centers for Disease Control and Prevention Atlanta, Georgia, USA

    Statistics from

    The scientific community's quest for unbiased research received a strong boost from a recent policy amendment on randomised controlled trials (RCTs) in this journal. Henceforth, the status of allocation concealment will be clearly indicated in the abstracts along with that of blinding, so readers will have additional information by which to judge the internal validity of trials. In this editorial, I address the background of and rationale for these enhancements.


    Random allocation to intervention groups remains the only method of ensuring that the groups being compared are on an equivalent footing at study outset, thus eliminating selection and confounding biases. This technique has allowed RCTs to play a key role in advancing medical science.

    The success of randomisation depends on 2 interrelated processes.1, 2 The first entails generating a sequence by which the participants in a trial are allocated to intervention groups. To ensure the unpredictability of that allocation sequence, investigators should generate it by a random process. The second process, allocation concealment, shields those involved in a trial from knowing upcoming assignments. Without this protection, investigators and patients have been known to change who gets the next assignment, making the comparison groups less equivalent.36

    For example, suppose that an investigator creates an adequate allocation sequence using a random number …

    View Full Text

    Request Permissions

    If you wish to reuse any or all of this article please use the link below which will take you to the Copyright Clearance Center’s RightsLink service. You will be able to get a quick price and instant permission to reuse the content in many different ways.