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Blind Study: Definition & Explanation

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  • 0:00 The Need for Blind Experiments
  • 0:57 Control and…
  • 2:05 Single-Blind Experiments
  • 3:37 Double-Blind Experiments
  • 5:11 Lesson Summary
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Lesson Transcript
Instructor: Tiffany Frye
Biases of research subjects and researchers can lead to flaws that make research results invalid. Complete this lesson to find out how using blind studies can eliminate these biases and lead to more robust research results.

The Need for Blind Experiments

If you were asked to taste coffee from your favorite local coffee shop and coffee from an unknown source and give your opinion on which was better, chances are you would choose the one you had a personal attachment to - the coffee from your favorite shop. If these taste-test results were recorded, they would likely result in an unfair judgment of the two different coffees because of your personal bias.

But what if the coffee were served in anonymous mugs, and you didn't know which coffee was which? You might still choose the coffee from your local coffee shop, but you might choose the unknown coffee. Whichever one you chose, the results could be trusted to be more valid because your bias would have been removed. Conducting blind experiments removes the bias of the research subjects (and sometimes also the researchers themselves), thereby helping to avoid biases in results.

Control and Experimental Groups

Scientific experiments are usually structured with a control group and an experimental group. The control group is the neutral group - they do not receive the treatment or have any other experimental condition applied to them. The experimental group, or treatment group, receives the treatment or other variable. A control group is necessary in order to test the effects of the experimental variable on the experimental group.

For example, say a researcher wanted to test the effects of eating a chocolate candy bar on memory. If the researcher only had one group eating a candy bar and then taking a memory test, he or she would have nothing to compare the results to in order to determine if the candy bar affected the research subjects' performance on the test. However, if the researcher has another group who eats nothing at all or does something presumably neutral, like drinking a glass of water, and this group also takes the memory test, then the researcher has something to compare the results to. Having a control group allows the researcher to draw a conclusion from the results of the experimental group.

Single-Blind Experiments

The word 'blind' in 'blind experiment' refers to the fact that the research subjects and possibly the researchers themselves are unaware of which group, control or experimental, the research subjects are in. In the case of single-blind experiments, it is only the research subjects who are kept unaware of their status as members of the control or experimental groups.

This is a useful experimental design if the researchers must be aware of who is in which group. For instance, if the researchers are doctors comparing the effects of a surgery with a placebo, there is no way to hide the knowledge of who is in what group if the researchers are the ones performing the surgery or placebo sham surgery (a procedure in which the patient thinks he or she is undergoing surgery but in reality is not).

Single-blind experiments should be avoided in experiments where there is a risk of experimenter bias. Experimenter bias is most likely to be a factor when the experimenter has an idea about how he or she would like the results to turn out or when there is a risk for subjective interpretation of the results.

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