What is the primary goal of blinding in clinical trials?

The primary goal is to reduce bias, particularly observer bias, interviewer bias, and subject expectation bias, which can affect reported outcomes and the interpretation of results.

Are there different levels of blinding?

Yes, common levels include single-blinding (patient unaware), double-blinding (patient and investigator unaware), and triple-blinding (patient, investigator, and outcome assessor unaware).

How can blinding be maintained when a device is clearly visible?

Strategies include using sham procedures, identical-looking inactive devices, or, more commonly, blinding outcome assessors who are not involved in the procedure or direct patient care.

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Clinical & TrialsClinical Evidence

Blinding and Masking

Procedures that hide treatment assignment from patients, investigators, or assessors to reduce bias.

Reviewed by Christian Espinosa, Founder, Blue Goat CyberLast reviewed May 5, 2026

Definition

Single-, double-, and triple-blinding apply progressively to patients, investigators, and outcome assessors. Device trials often achieve only assessor-blinding due to the visible nature of devices/procedures. When patients and operators cannot be blinded, trials often use blinded independent assessors, core labs and clinical events committees to reduce bias. Sponsors document the blinding approach in the clinical investigation plan and check blinding success where possible. Unblinding procedures for emergencies must be defined so safety is not compromised.

What the regulation says

Blinding and masking are critical study design elements emphasized by regulatory bodies like the FDA in their guidance on clinical trials for medical devices, particularly to minimize bias. The EU MDR, in Annex I, Section 21.2, also stresses the importance of appropriate statistical methods and study design to ensure the scientific validity and reliability of clinical data. These practices aim to ensure objectivity in assessing treatment effects and patient outcomes.

What this means in practice

Independent core labs and blinded adjudication committees are standard mitigations for device trials where full blinding is impossible.

Examples

A clinical trial for a novel implantable glucose monitor might blind the patients to whether they received the active device or a similar-looking placebo device that does not provide glucose readings.
In a study evaluating a surgical robot, the surgeons and patients may not be blind, but the outcome assessors evaluating post-operative complications and recovery time can be blinded to the treatment arm.
A study comparing two different drug-eluting stents might anonymize the stent type in patient records and blind the radiologists interpreting follow-up angiograms to stent assignment.

Common pitfalls

•Failure to document the rationale for the chosen blinding level can lead to regulatory scrutiny.
•Inadequate blinding procedures can compromise the scientific validity of clinical trial results, leading to questions from regulatory authorities.
•Assuming that device trials cannot be blinded at all, rather than seeking opportunities for partial blinding, is a common pitfall.
•Not accounting for potential unblinding events and having a plan to address them can undermine study integrity.

Frequently asked questions

Blinding is challenging due to the visible nature of devices, the need for clinician interaction during procedures, and the distinct characteristics of device interventions compared to pharmaceutical products.

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Clinical & Trials

Core Laboratory

An independent, centralized laboratory that performs standardized, blinded analysis of imaging or physiologic data from multiple trial sites to produce consistent endpoint adjudication.

Clinical & Trials

Sham Control

Placebo-equivalent for device trials - a non-therapeutic procedure that mimics the investigational intervention.

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Sources

3 sources

Every citation below opens the original document. Each is graded against our source-tier hierarchy so you can see what rests on binding law versus commentary.

Tier 1Binding law and standards· 1Tier 2Regulator guidance and consensus· 2

Link health: 3 verified· last checked 2026-06-20

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Category: Clinical & Trials
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Procedures that hide treatment assignment from patients, investigators, or assessors to reduce bias.

·Independent core labs and blinded adjudication committees are standard mitigations for device trials where full blinding is impossible.
·Device trials often achieve only assessor-blinding due to the visible nature of devices/procedures.
·When patients and operators cannot be blinded, trials often use blinded independent assessors, core labs and clinical events committees to reduce bias.

Remember this

Watch out: Failure to document the rationale for the chosen blinding level can lead to regulatory scrutiny.

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