What is it? Why is it important?

In studies, blinding is the act of concealing a study treatment allocation from participants, researchers, or both.

The aim of blinding is to minimize bias and enhance the validity of the study.


Biases include:

  • An observer bias, where a researcher has a certain expectation towards the effectiveness of a study intervention


  • An analysis bias, where the statistician has some expectation regarding the results of a study



Study blinding can either be:

  • Single-blinded, where only the participant is unaware of the treatment allocation
  • Double-blinded, where both participants and researchers are unaware of the treatment allocation

What do I need to do?

As a SP-INV, define the blinding of your study by specifying:

  • The type of blinding (i.e. do you want to blind the participants, the researchers (e.g. SP-INV, Site-INV, the statistician, everyone?)
  • Measure(s) implemented to ensure blinding (e.g. indistinguishable packaging of the placebo and intervention medication blinding both participants and of the person delivering the medication).
  • The feasibility to implement and maintain blinding procedures during study conduct and analysis


Blinded studies may require more resources (e.g. study staff, production and management of investigational product). In order to avoid accidental unblinding, double-blinded studies pose additional challenges and require additional planning (e.g. procedures to ensure participants, site staff, and statistician remain blinded during study conduct and the analysis of study results)

Where can I get help?

Your local CTU can support you with experienced staff regarding this topic


ICH Topic E9 statistical Principles for Clinical Trials – see in particular

  • 2.3.1 Blinding

ICH Topic E8(R1) on general considerations for clinical studies - see in particular

  • 5.5 Methods to reduce bias
  • CTU – Clinical Trials Unit
  • ICH – International Council for Harmonisation
  • Site-INV – Site Investigator
  • SP-INV – Sponsor Investigator
Basic ↦ Statistics ↦ Study Design ↦ Study Blinding

Provides some background knowledge and basic definitions

Basic Monitoring
Basic Drug or Device

Starts with a study idea

Ends after having assessed and evaluated study feasibility

Concept Drug or Device

Starts with confidence that the study is feasible

Ends after having received ethics and regulatory approval

Development Drug or Device

Starts with ethics and regulatory approval

Ends after successful study initiation

Set-Up Ethics and Laws
Set-Up Quality and Risk
Set-Up Drug or Device

Starts with participant recruitment

Ends after the last participant has completed the last study visit

Conduct Drug or Device

Starts with last study visit completed

Ends after study publication and archiving

Completion Statistics
Completion Drug or Device
Current Path (click to copy): Basic ↦ Statistics ↦ Study Design ↦ Study Blinding

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