In the medical field, it is unethical to not inform your patient of a process or a procedure you want to carry out on them. It is required that the patients are informed about the treatment they would be given and that they consent to it. 

However, there is a method known as the blind study in psychological research.  A blind study prevents the participants from knowing about their treatment to avoid bias in the research.

This article will focus on the double-blind study which is a type of blind study which leaves both the researcher and the participants in the dark about important details of the study. That way the research is expected to be bias-free and far from any external influence.

The blind study has no ground in patient-doctor physical therapy sessions, but it is very helpful in other studies such as pharmacological research.

This is why we will consider a double-blind study, its usefulness, advantages, and disadvantages in a study or research. 

What is a Blinded Study?

A blinded study is research conducted in a way that prevents the subjects ( blind the subjects) from knowing the treatment they are given so that the researcher is guaranteed a biased free result. Information that can influence the subjects of a research is withheld from the subjects until the completion of the research.

If good blinding is carried out on the subjects, it can eliminate any form of biases that may arise from the subjects’ expectations, influence from the researcher, researcher’s bias, and other forms of biases that may occur in a research test.

This can be achieved as a blind study can be imposed on all participants in research. From the researcher to the subjects, the analysts, and even the judges or evaluators.

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In some cases, however, imposing blind study in research may be impossible or even unethical. For example, it is unethical for a medical practitioner to blind a patient from knowing their treatment. The ethical thing to do is let your patient be informed about a major part of their treatment if it’s in a face-to-face intervention.

A subject can become unblinded during a study if they obtain information that has been previously shielded away from them. For example, if due to experiencing some side effects symptoms, a subject could correctly guess the treatment he/she has been exposed to. The subject then becomes unblinded. Subjects becoming unblinded mostly occur in pharmacological testings. 

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What is a Double-blind Study?

Double-blind refers to a study or research where both the subjects or participants of a study and the researchers are oblivious of the treatment being given and the subjects receiving the treatment. Both the participants and the experimenter are kept in the dark. This is done to eliminate all presence of biases in the outcome of the research.

It is most useful in research because of the placebo effect.

For example, if a researcher wants to conduct research on the effects of a newly introduced drug. A double-blind study requires that both the researcher and the subjects are unaware of the process.

So the researcher that is analyzing the subjects would have no information about the subjects receiving the new drug (which is the treatment group) and those who are not receiving the drug (which is the control group).

Now if the participants are not aware of their treatment and the researcher is not provided with information on who is receiving the treatment, the question that requires an answer is, why is a double-blind study needed?

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Purpose of a Double-blinded Study

Every procedure has its purpose and a double-blind study is not left out. The purpose of a double-blind study is to make sure that the outcomes of a study are free from biases. Using the double-blind method in a study improves the level of credibility and validity of the study 

A double-blind study is used in the scientific field, psychologists, and also in the legal process.

Read more: What are Cross-Sectional Studies: Examples, Definition, Types

Types of Blinded Studies

There are three types of blind studies namely single-blind study, double-blind study, and triple-blind study

1. Single-blind study: in this type of blind study only the subjects in the experiment are prevented from knowing the treatment they are given. The single-blind study is also known as the single masked study.

2. Double-blind study:  In the double-blind study both the subjects or participants and the researcher are blinded.  The researcher is unaware of who is receiving what treatment and the participants are unaware of the treatment they are receiving.

3. Triple blind study: here in the triple-blind study the participants, the researcher analyzing data, and the data collector are blinded from the information about the study. These three groups are prevented from knowing the treatments being given out or being received.

When to Use Each Type of Blind Study

Now that we know the types of blind study we are going to consider when it is appropriate to use either of these types of blind study in research.

  • When to use a single-blind study

A single-blind study is usually conducted to prevent the subject from being aware of the treatment being studied. This is in case they get influenced and that leads to bias in the outcome.

It should be noted that there are cases where blinding a participant or patient is considered unethical. Therefore, single-blind study should only be used in statistical research or studies that don’t involve physical therapy between a patient and a doctor.

  • When to use a double-blind study

Double-blind study is conducted when both the participants and the researcher are not allowed to know details of the research. This process is used to prevent bias in the study results and when there is a need to understand the characteristics of the results or to understand placebo effect.

  • When to use a triple-blind study:

Use triple blind study if you aim to reduce your study and improve the accuracy of your results. This is because a triple-blind study allows randomization where the treatment item and the intervention are not known to the participants, researcher, data collector, or clinical personnel.

Read: Survey Errors To Avoid: Types, Sources, Examples, Mitigation

Advantages of Double-blinded Study

The following are the advantages of double-blind study:

1. It tests for three groups

The double-blind study usually involves three groups of subjects. The first is the treatment group, then the placebo, and lastly, the control group. The treatment group and the placebo are given the test item even though the researcher wouldn’t know which group is getting the treatment. No test item is administered to the control group because they are used as a basis of comparison for the results of the treatment group and the placebo.

If there’s a significant improvement in the placebo group over the control group, then it is considered that the treatment administered worked.

2. Reduces experimental bias

A double-blind study reduces the risk of biases in research. Biases can occur when a researcher influences the outcome of a study directly or otherwise. However, because the researcher is often also in the dark, it is difficult to influence the study.

This allows for credible, reliable, and valid research results.

3. Result duplication

The results of a double-blind study can be duplicated and that is why this procedure is considered one of the best practices. A double-blind study allows other researchers to follow up with the same processes, apply the test item, and compare the result with the control group.

The usefulness of this method is that if the results from these studies are close, it proves the validity of the test item that was administered. If there is no duplication in the research results, another study has to be carried out to determine why.

Disadvantages of a Double-Blind Study

1. It is expensive

One huge disadvantage of a double-blind study is that it is expensive to conduct. It takes several months or years to complete because the researcher has to examine all the possible variables and they may have to use different groups to gather enough data. 

Many corporations after estimating the cost of this study which runs into millions of Dollars might have to spread the research across multiple months. Even for government studies, conducting this study may run into billions of dollars thereby making the medicine expensive in the market. This is one of the reasons why new prescription medicines are sold at an expensive price in the market.

2. Low representation

A double-blind study cannot provide a properly represented sample group because it is small. Most double-blind study is designed to enroll at least 100 people or participants for the research however the most preferable number is 300. It is true that the effectiveness of a treatment can be proven even in small studies but more people or participants are required to determine a pattern in research so that the results can be properly analyzed and verified.

Research generally requires participants in large numbers to participate in the trials and progress of a treatment being administered or in plan to be introduced to the market.

This is because even when the product or treatment item has gotten to the third phase of testing it still has only a 60% chance to proceed to another stage.

3. Negative reaction

In some cases some of the participants may react negatively to the treatment item when this happens the results from the test can be compared to see what changed. Some participants may react negatively to the placebo which may lead to producing some side effects that may make it seem like they were receiving the treatment item when they did not.

4. Time factor

Many times it is almost impossible to complete a double-blind study. For example, you cannot keep the subject or participants of a psychotherapy experiment in the dark about who gets the treatment item and who doesn’t get the treatment item. Double-blind study can only work in this scenario if you find a way to provide two similar procedures without each of the groups communicating about which group is getting the treatment item and which group is getting the placebo.

Frequently Asked Questions about Blind Studies

  • Which is better: single-blind or double-blind study?

To determine which is best between a single-blind study and a double-blind study the case being studied has to be considered.

For example, if a researcher is conducting a study on the effects of a medicine that can cure Alzheimer’s, it is best to use a double-blind study rather than a single-blind study. This is because the participants will be unaware if they received the treatment item from the real drug or if they received the placebo which in turn reduces any external influence on the results of the test.

  • When would you use a single-blind study?

Use a single-blind study if the participants having knowledge of the group they belong to might result in bias. I.e. whether their being aware of the treatment item and the questions of the study might result in bias.

  • What is the difference between a single and double-blind study?

The significant difference between a single study and a double-blind study is that in a single-blind study only the participants or the patient are blinded while in a double-blind study both the participant and the researcher are blinded.


In any study, it is good to know how the results of the treatment group and the response group compare in an experiment. This is why a double-blind study is important. 

The risk of anyone manipulating data or influencing the participants is averted since a double-blind study prevents both the researcher or the participants from obtaining in-depth knowledge of the study.

You can be assured that the researcher cannot accidentally communicate with the subjects or participants. Now that is one huge importance and psychological benefit of the placebo effect.

  • busayo.longe
  • on 10 min read


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