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Allocation concealment aims to prevent knowledge of the next assignment from influencing participant selection. An open-label design does not make advance predictability necessary or acceptable simply because treatment becomes visible later.
Define the question and assumptions
Map when eligibility becomes final, when allocation is requested and when treatment is revealed. Examine not only permissions but also numbering patterns, packaging and system messages that might leak information. Treat concealment before assignment and blinding after assignment as different controls with different failure modes.
Hypothetical study example
In a hypothetical open-label trial, a site employee reports predicting the next arm from available pack numbers. The team investigates whether enrolment order could have been influenced and reviews supply processes. Lack of access to the formal randomisation screen is not treated as sufficient reassurance.
Design review checks
- Document how eligibility is confirmed before an allocation request is submitted.
- Test whether packaging or messages allow users to infer a forthcoming assignment.
- Review cancelled and repeated allocation requests together with their recorded reasons.
Record the decision and its limits
Acceptance should use scenarios showing that a person cannot obtain the upcoming allocation for someone not yet enrolled. Investigate suspected leaks alongside their possible effects on selection and data. Necessary treatment access for safety remains available through a separate controlled and justified process.
Frequently asked questions
- Does an open-label design remove concealment needs?
- No. Visibility after assignment differs from concealment before assignment.
- Is a strong password sufficient?
- No. Packaging, printouts and operational communications can also disclose allocation information.