Double Blind Study (Definition + Examples)

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The impact of many treatments can only be confirmed after their effect has been verified in a double-blind study.

What Is a Double-Blind Study? 

A double-blind study is an experiment where both researchers and participants are “blind to” the crucial aspects of the study, such as the hypotheses, expectations, or the allocation of subjects to groups. In double-blind clinical trials, neither the experimenters nor the participants are aware of who is receiving a treatment.

Why Do a Double-Blind Study?

The main purpose of double-blind studies is to minimize the effects of experimenter bias. In other words, the results of the research are less likely to be affected by external factors, such as the experimenters verbally or nonverbally communicating their assumptions about the treatment’s efficiency or the expectations of the participants.

Double-blind studies serve as an invaluable scientific method in the pharmaceutical industry trials where they are regularly used for determining the impact of new medications. Double-blind studies are the very foundation of modern evidence-based medicine. They are often referred to as the gold standard for testing medications, that is, the most accurate test available. 

While they are best known for their application in medicine, double-blinded studies are widely used to validate theories and ideas in many other fields including agriculture, biology, chemistry, engineering, forensics, and social sciences. 

Example of Double-Blind Study

Identifying successful treatments is a complex procedure. Let’s say that a physician prescribes a new medication to a patient. After taking the medication, the patient reports improvement in his or her condition. Yet this doesn’t simply mean that the treatment is effective. In fact, in many cases patients will see improvements even when they are not taking active medication. 

In order to properly test the medication, a double-blind study will have to take place in which the experimenter (acting as the physician) administers either the medication or a placebo to the participant (acting as the patient). Only a third-party knows whether the medication was real or not. The participant's answers about their treatment will be recorded and sent to that third party.

Double-blind studies aren't just used to test new medication. A double-blind study was used to see if airport security dogs could sniff out COVID!

Double-Blind Studies and Placebo Effect

The placebo effect is a crucial component of double-blind studies. 

A placebo is an inactive substance that has no effect on the individual who is taking it. It looks just like the medication that is being tested so that the participants can’t say whether they are receiving the treatment or not. 

How to Conduct a Double-Blind Study

Subjects in double-blind studies are typically divided into three different groups: treatment or experimental group, placebo group, and control group. 

Participants who are not receiving any treatment are placed in the control group. This group serves as a baseline for determining whether the medication in question has any significant effects. If the control group gets better over time, then this improvement will set a standard against which the other two groups are compared. 

People placed in the treatment group are given the actual medication, while subjects in the placebo group are offered a placebo pill. Neither the participants in the treatment and placebo groups nor the experimenters have the information on who is receiving the real drug.

At the end of the trial, data collected from the groups are compared to determine if the treatment had the expected outcome. If subjects in the placebo group fare better than the control group, this positive development can be attributed to the participants’ belief that the pill works. But if people in the treatment group improve more than those in the placebo one, then the results can be attributed to the effect of the medication.

Other Types of Blind Studies

Several different types of blind studies are being used in research, such as double-blind comparative studies, single-blind studies, and triple-blind studies.

Double-blind comparative studies

In double-blind comparative studies, one group of participants is given a standard drug instead of a placebo. These studies compare the effects of new medicine and an old one whose impact has already been proven. This kind of study is useful in determining whether a new treatment is more effective than the existing one. 

Single-blind studies

In single-blind studies, only the participants are not informed whether they are receiving the real treatment. The experimenters, on the other hand, know which participants belong to which group.  

Triple-blind studies

Triple-blind studies are clinical trials in which knowledge about the treatment is hidden not only from subjects and experimenters but also from anyone involved in organizing the study and data analysis. 

Limitations of Double-Blind Studies

Despite their significance, double-blind studies hold a number of limitations and are not applicable to every type of research.

Number of Participants

To be effective, a double-blind study must include at least 100 participants and preferably as many as 300. Although effective treatments can also be proven in some small-scale trials, many double-blind studies are too limited in size to provide a representative sample and establish meaningful patterns. Studies involving fewer than 30 participants generally can't provide proof of a theory. 

Types of Double-Blind Studies 

Double blinding is not feasible in all types of trials. For instance, it is not possible to design studies on therapies such as acupuncture, physical therapy, diet, or surgery in a double-blind manner. In these cases, researchers and participants can’t be kept unaware of who is receiving therapy.

Nocebo Effect

Participants in clinical trials must be informed of the possible side effects that may result from the experimental treatment. However, the mere suggestion of a negative outcome may lead to the adverse placebo effect, also known as the nocebo effect. It can result in participant dropouts and the need for additional medications to treat the side effects.

In research, the use of a placebo is acceptable only in situations when there is no proven acceptable treatment for the condition in question. For ethical reasons, participants must always be informed of the possibility that they will be given a placebo. As a consequence, some participants may think that they feel the effects of the placebo, which makes them believe that they are in the treatment group. This high positive expectancy is a disadvantage that can lead to a misinterpretation of the results.

Costs of Double-Blind Studies

Double-blind procedures are very expensive. They may take several months to complete, as experiments often require numerous trials using different groups in order to collect enough data. As a result, double-blind studies can cost up to several million dollars, depending on the amount of work required and the industry in which the product is being tested.

Reference this article:

Practical Psychology. (2020, June). Double Blind Study (Definition + Examples). Retrieved from

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