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Academy · Research Writing · Blinding and masking
Blinding and Masking in Clinical Trials: Blinded Parties and the Biases Each Level Addresses
The term “double-blind” is often used as a single marker of rigour, but blinding has distinct levels; the identity of the blinded parties matters because each level protects against a different source of bias.
Blinding (or masking) means concealing treatment-group assignment from one or more parties in a trial. Different parties — participants, treating clinicians, outcome assessors, data analysts — can each be blinded or not, and each layer protects against a distinct, specific source of bias.
Learning objectives
- Which parties can be blinded, and which specific bias each layer protects against.
- Why “double-blind” is an ambiguous term unless the blinded parties are named.
- When blinding is genuinely not feasible, and what to do instead.
Common misconceptions
- “‘Double-blind’ always means the same two parties are blinded.” Karanicolas, Farrokhyar and Bhandari note that “double-blind” has been used inconsistently across the literature to refer to different combinations of blinded parties, which is why current reporting guidance asks trials to name explicitly who was blinded (participants, care providers, outcome assessors, data analysts) rather than relying on the ambiguous term alone.
- “A trial that cannot blind participants cannot be rigorous.” Some interventions (such as surgery versus no surgery) cannot feasibly blind participants or treating clinicians, but outcome assessors and data analysts can often still be blinded — Karanicolas and colleagues note that blinding whichever parties are feasible, and being transparent about which could not be, is the correct response, not abandoning rigour altogether.
Parties that can be blinded
Karanicolas and colleagues identify the parties a trial can potentially blind: the participants themselves, the clinicians delivering care, the people assessing outcomes, and the data analysts conducting the statistical analysis1. A trial can blind any combination of these parties, and the specific combination should be stated by name rather than summarised as “single-blind”, “double-blind” or “triple-blind”, terms that the authors note have been used inconsistently across the literature.
Biases addressed by each level of blinding
Each blinded party protects against a distinct bias: blinding participants reduces performance bias from differential expectations or behaviour; blinding treating clinicians reduces differential co-intervention or care; blinding outcome assessors reduces detection bias, particularly for subjective outcomes; blinding data analysts reduces bias in analytic choices made with knowledge of which group benefited1. The loss of one layer does not necessarily compromise the others: an outcome assessor can remain blinded even when participants cannot be.
Alternatives when blinding is not feasible
Surgical, behavioural and some device trials often cannot blind participants or treating clinicians to which arm a person is in. Karanicolas and colleagues recommend that in these cases, trials should still blind whichever parties remain feasible — particularly outcome assessors, especially for subjective outcomes — and report clearly which parties could not be blinded and why, rather than either overstating the trial’s blinding or abandoning the concept altogether1.
Key points
Key points
Blinding should be reported by naming exactly which parties — participants, clinicians, outcome assessors, analysts — were blinded, because each layer protects against a different, specific bias, and the term “double-blind” alone does not convey that.
Practical application
Practical application
- Name the blinded parties explicitly rather than a blinding-level label. Authors should state exactly who was blinded (participants, clinicians, outcome assessors, analysts), in accordance with CONSORT, rather than relying on “double-blind” alone.
- Blind outcome assessors even where participant blinding is infeasible. For surgical or behavioural interventions, priority should be given to blinding the person who assesses the outcome, particularly for subjective measures.
- Report explicitly where blinding was not possible, and why. The parties that could not be blinded, and the reason, should be stated rather than the limitation being omitted.
Frequently asked questions
Not automatically. Its quality depends on whether feasible blinding (such as of outcome assessors) was still implemented and on how susceptible the specific outcome is to bias from unblinding; an open-label trial with objective, hard outcomes (such as mortality) is less vulnerable than one with subjective outcomes.
Yes. Analysing data with treatment-group labels concealed (for example, as “Group A/Group B”) until the primary analysis is finalised is a recognised practice, independent of whether participants or clinicians remain blinded.
No. Blinding addresses specific biases (performance and detection bias) but does not address selection bias, attrition bias or other biases, which require their own reporting and mitigation.
References
- Karanicolas PJ, Farrokhyar F, Bhandari M. Blinding: Who, what, when, why, how? Canadian Journal of Surgery. 2010;53(5):345-348. read 10 October 2026. View on PubMed Central
Every source above is a peer-reviewed article, a publisher’s record of one, or a standard issued by the body that owns it. Each carries the date it was last read. Where a standard moves, this article is revised rather than left up with a note.
How to cite this article
Pick your referencing style and copy it. Your university or target journal may vary the punctuation — check its guide if it has one.
Pubrica Academy. (2026, October 10). Blinding and Masking in Clinical Trials: Blinded Parties and the Biases Each Level Addresses. Pubrica. https://pubrica.com/academy/concepts-definitions/blinding-and-masking-levels/
Pubrica Academy. “Blinding and Masking in Clinical Trials: Blinded Parties and the Biases Each Level Addresses.” Pubrica, 10 Oct. 2026, pubrica.com/academy/concepts-definitions/blinding-and-masking-levels/.
Pubrica Academy (2026) Blinding and Masking in Clinical Trials: Blinded Parties and the Biases Each Level Addresses. Pubrica. Available at: https://pubrica.com/academy/concepts-definitions/blinding-and-masking-levels/ (Accessed: 15 October 2026).
Pubrica Academy. “Blinding and Masking in Clinical Trials: Blinded Parties and the Biases Each Level Addresses.” Pubrica. October 10, 2026. https://pubrica.com/academy/concepts-definitions/blinding-and-masking-levels/
Pubrica Academy, ‘Blinding and Masking in Clinical Trials: Blinded Parties and the Biases Each Level Addresses’ (Pubrica, 10 October 2026) <https://pubrica.com/academy/concepts-definitions/blinding-and-masking-levels/> accessed 15 October 2026.
Pubrica Academy. Blinding and Masking in Clinical Trials: Blinded Parties and the Biases Each Level Addresses. [Internet]. Pubrica; 2026 Oct 10 [cited 2026 Oct 15]. Available from: https://pubrica.com/academy/concepts-definitions/blinding-and-masking-levels/
Pubrica Academy, “Blinding and Masking in Clinical Trials: Blinded Parties and the Biases Each Level Addresses,” Pubrica, Oct. 10, 2026. [Online]. Available: https://pubrica.com/academy/concepts-definitions/blinding-and-masking-levels/
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author = {{Pubrica Academy}},
title = {Blinding and Masking in Clinical Trials: Blinded Parties and the Biases Each Level Addresses},
howpublished = {Pubrica},
year = {2026},
month = {oct},
url = {https://pubrica.com/academy/concepts-definitions/blinding-and-masking-levels/},
note = {Accessed: <span data-cite-acc="iso">2026-10-15</span>}
}This article is written to be learned from. Cite it if you are referring to what it says; if you are using the evidence behind it, cite the sources listed above instead.
Blinding reporting check
Use when writing the methods section's blinding statement.
[ ] Each party's blinding status named explicitly (participants, clinicians, outcome assessors, analysts) [ ] Where blinding was infeasible, the reason stated [ ] Outcome-assessor blinding prioritised where participant blinding was not possible [ ] Susceptibility of the specific outcome to unblinding-related bias discussed
Pubrica AcademyWritten and maintained by Pubrica’s subject matter experts. Articles are revised when the underlying standards change, and each article states the date on which it was last reviewed.
How Pubrica can help
Pubrica assists in drafting blinding statements that name each party explicitly, in accordance with CONSORT and the requirements of the target journal.