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What is a Double Blind Test?

Mary McMahon
Updated May 21, 2024
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A double blind test is a scientific test in which neither test subjects nor administrators know who is in the control group and who is in the experimental group. The intent is to create an unbiased test environment, ensuring that the results of the testing are accurate and will stand up to analysis by other members of the scientific community. The concept of a double blind test is an excellent example of the scientific method, since it aims to be entirely objective and potentially repeatable.

Basics of Clinical Trials

Before delving into the details of a double blind test, it helps to understand how scientific testing is typically administered. For our purposes, we will use a test of a new pharmaceutical product as an example, although such testing can also be performed to research other matters of interest in fields such as psychology. The goal of the test is to determine whether or not the medication is effective, and what the side effects of the medication may be.


One could simply offer the medication to a group of people and look at the results, but most drug testing involves the use of a placebo, or false drug. A placebo is a substance which appears to be an actual drug to a casual observer but has no physical effect on the body. The test subjects are carefully selected to ensure that they are at more or less the same level of health, and then divided into two groups. One group, the control group, receives a placebo while being told that it is the real substance under test, while the other group, the experimental group, receives the actual drug. Results between the two groups are compared to see if the substance under test has any measurable effects, useful or otherwise.

Typically, such a test is “blind,” meaning that test subjects do not know whether they are in the control group or the experimental group. This is intended to eliminate bias on the part of the test subjects, who may respond differently if they know which group they are in. In a double blind test, the researchers performing the testing also do not know who is in which group. This eliminates observer or experimenter bias, as experimenters may unwittingly bias participants because they expect them to respond in a particular way. The double blind test is an industry standard for many pharmaceutical tests.

Double Blinding

To administer a double blind test, a separate coordinator assigns the test subjects random numbers and divides them into two groups. Each subject is given a unique code which is known only to the coordinator. This coordinator also provides the drug to be administered. At the end of the trial, the researchers are given the code so that they can begin to interpret the results.

Using a double blind test method can ensure that test results are valid and more widely accepted by the general scientific community. It tends to cost more to administer a double blind test, because of additional paperwork and processing, but many scientists feel that this cost is well worth the benefits. In an even more elaborate situation, a triple blind test, the statistician examining the results is also kept in the dark about the identities of experimental and control group members.

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Mary McMahon
By Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a All The Science researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

Discussion Comments

By anon206182 — On Aug 15, 2011

The blindfolded taste test would probably not qualify as a double blind test, because the people placing the products on the table know what they are. The tasters may have some idea that one of the samples is going to be Pepsi and the other one will be Coke, so they might have some preconceived notions about which one is better, too.

In order for a soft drink taste test to be truly double blind, the people passing out the samples would also have to be kept in the dark about which was which.

By liveoak — On May 04, 2011

When they do taste tests of products, and they blindfold the contestants, isn't that considered a double blind taste test? I have seen this on television regarding soft drinks.

By robert13 — On May 01, 2011

I've heard of this before but never knew what it meant. Being an epileptic, I was asked by my neurologist to participate in a test but I wanted to be sure of the testing methods behind it after having been on so many medications with bad side effects. I didn't end up taking the test because I didn't fit the criteria but I'll keep this in mind in case I get asked again in the future and be sure to ask whether it's a single blind or double blind study.

Mary McMahon

Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a...

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