What is Blinding?

 

In clinical research, “Blinding” refers to the approach of keeping participants, researchers, or both unaware of the treatments assigned to the participants. “Blinding” is closely related to Randomized Controlled Trial (RCT) described earlier and is a key method to improve the quality of RCT.  The two most common blinding methods are “Single Blinding” and “Double Blinding”:

 

Single Blinding

• It refers to the trial course in which only the participants are unaware of their assignments to the “Experimental Group” or “Control Group”, while the researchers know. 

 

• It aims to prevent psychological factors of the participants from influencing treatment outcomes. In the absence of blinding, participants’ knowledge of their assigned treatments may influence their behaviours and responses to outcome measurements, particularly for subjective endpoints (e.g. self-reported pain relief).  However, blinding is less important for objective endpoints (e.g. tumor size reduction assessed by imaging).

 

Double Blinding

• It refers to the trial course in which neither the participants nor the researchers are aware of the treatment assignments.

 

• It aims to minimize bias on both parties and ensure objective data collection, especially to reduce researchers' subconscious influence on disease assessment, patient care, and data analysis etc. due to a desire for positive results. This type of blinding is commonly used in drug trials.

 

Adoption of blinding usually depends on the study design, resources available and ethical considerations.  Generally speaking, blinding helps minimize bias and maximize validity of results.  While inadequate blinding may compromise objectivity and reliability of a study.

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Reference：

Helene M, Gemma L C, Hayley E J, et al. Impact of blinding on estimated treatment effects in randomised clinical trials: meta-epidemiological study. BMJ. 2020;368:l6802. doi:10.1136/bmj.l6802