Double-Blind Study: Definition & Explanation

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  • 0:01 Control & Experimental Groups
  • 1:36 Conducting Blind Experiments
  • 2:28 Double-Blind Experiments
  • 3:53 When They Can't Be Used
  • 4:42 Lesson Summary
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Lesson Transcript
Instructor: Tiffany Frye
Double-blind studies are an important part of conducting research. Learn how double-blind studies contribute to the validity of research by reducing the biases of research participants and the experimenters themselves.

Control Groups and Experimental Groups

When researchers design experiments, they typically break the participants into two groups: a control group and an experimental group. The control group of participants does not receive the experimental treatment. In contrast, the experimental group is the group that participates in the experimental part or actually receives an experimental treatment.

Both groups are equally important to the success of the experiment. Without a control group, researchers would have nothing to compare the results of the experimental group to, and so they wouldn't be able to determine if the experimental treatment had produced any significant effect.

Imagine you are participating in an experiment to determine if drinking a sports drink makes you feel more energetic than drinking water. If you only drink sports drinks, you have no way to compare it to how water makes you feel. You need to measure the effects of both sports drink, which is your experimental group, and water, your control group, and then compare the results.

When dealing with human subjects, researchers can't simply tell some participants to be in the control group and some to be in the experimental group. Human behavior is complex, and it turns out that people act differently depending on which group they are in. That is, if they 'know' which group they are in. When researchers realized that knowing which group they are in affects how participants act and thus renders results invalid, they devised a method of conducting experiments called a blind experiment.

Conducting Blind Experiments

Image of a sports drink

Let's imagine you are still testing the effectiveness of sports drinks versus water. If you are aware of the experiment's aim and consume a sports drink, you may subconsciously convince yourself that you feel more energetic. This is called participant bias, and it occurs when participants behave how they believe the researcher wants them to behave.

The best way to avoid participant bias is to perform a blind experiment. These kinds of experiments don't inform participants which group they are in, so that knowledge can't influence their behavior. So, instead of receiving a drink that is obviously a sports drink, you may receive a drink that appears to be water but has nutrients added to it so that it is equivalent to drinking a sports drink. This way, which group you are in is hidden from you; you are 'blind' to which group you are in.

Double-Blind Experiments

Experimenters also use double-blind experiments, which take into account not only participant bias but also experimenter bias. Experimenter bias occurs when a researcher unwittingly influences results by either administering the experiment or collecting and analyzing the data in a biased fashion. This can happen when the experimenter has a personal stake in the results of the experiment or when the nature of the experiment is particularly subjective, such as in psychology and other social sciences.

Let's look at an example. Imagine a taste-test experiment in which participants compare two popular soda brands to determine which is better. If the individual administering the test is employed by one of the brands, then he or she will probably have an interest in that brand winning the taste-test. This may lead him or her to put a bit more ice in the preferred soda or fill up one cup closer to the top.

A&W Cream soda
Sparletta Cream soda

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