Blinding and Masking

Blinding or masking in research refers to not informing the patients and/or the investigators about the treatment assessment. The reason for blinding and masking is to prevent subjective bias that can occur due to the knowledge of the assessment. The use of blinding and masking is most common in medical studies. Especially, when the outcomes of an intervention are studied.

There are three types of blinding and masking:

  • Single blind
  • Double blind
  • Triple blind

Each of the above mentioned type has its own purpose and significance. Also, each of these have shortcomings or weaknesses. For example, single blind refers to withholding knowledge of the assessment from participant. On the other hand, double blind refers to retaining knowledge from both participant and investigator. Lastly, the person administering the treatment is unaware. The researcher needs to clearly define in the research how and in what manner blinding or masking is used in the research. Because, the people involved in the research process will get clear idea about the blinding methods. As well as, the readers will understand and evaluate the authenticity of methods.


This method has several benefits for the research. Regardless of the fact that some researchers find it unethical. Some of the benefits are as fllows:

  • Subjects do not know about the intervention they do not introduce bias. There are many types of subject’s bias. And, it is difficult to know when the participant is biased. The participant can discontinue intervention. The subjects can show less cooperation, they can drop out.
  • Sometimes, as subjects know about the intervention they want to please the researcher or physician. They give positive response regardless of the actual outcomes.
  • The observer does not know about the intervention so observers’ bias is minimized. On the other hand, the observer can introduce subjectivity to the research.
  • Some topics are highly subjective and therefore, blinding is highly recommended. Otherwise, bias is inevitable from the patient or investigator side.
  • Data analysis is the most important part of the research. An unmasked data analyst can select favored responses. This can bring greater bias in the research outcomes.


Blinding and masking has some shortcomings and weaknesses. Also, it is not always possible to do it. Obviously, you cannot ignore the ethical concerns or health risks linked to such techniques. Although, there are various studies that are conducted to understand the difficulties in using this technique. These studies highlight the issues and provide guidance to overcome those issues.

  • You cannot use it when there are health concerns for the patient. For example, a patient who regularly takes a medicine cannot be given a placebo pill. The placebo pill can have worse effects on the health of the patient. Also, the patient may not apprehend it if it is in his knowledge.
  • It is not possible to do this when there are ethical concerns. The subjects may find it deceiving to stay unaware. In such studies the use of masking can put a question on the integrity of the study. In this case, it is better to use other bias-control techniques.
  • Some topics do not lend themselves to masking or blinding. Regardless of the fact that there is no risk or ethical concern involved.




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