Experimental Group: Definition & Explanation

Instructor: Lisa Roundy

Lisa has taught at all levels from kindergarten to college and has a master's degree in human relations.

An experimental group is used in an experiment to test a variable. It is the group to which the test variable is administered. Learn more about how an experimental group works in this lesson, and test your knowledge with a quiz at the end.

Definition of an Experimental Group

You usually store your microwave popcorn in the kitchen cabinet, but you read an article that recommends storing it the refrigerator. You want to find out if microwave popcorn actually pops better if it is stored in the refrigerator. You have two bags of popcorn so you keep one in the cabinet and place the other in the refrigerator. The next day you pop each bag of popcorn for the same amount of time in the microwave. You measure the amount of popcorn that popped in each bag to see which bag produced more.

You just created an experiment to test whether storing the popcorn in the refrigerator makes it pop better. In this example, your experimental group is the bag of popcorn you placed in the refrigerator. An experimental group is the group that receives the variable being tested in an experiment.

Experimental Groups in Action

There must be at least two groups in any valid experiment: The experimental group and the control group. The control group is the group in an experiment that does not receive the variable you are testing. For the experiment described above, the bag of popcorn that remained stored in the cabinet is the control group. The only difference in the two groups is where the popcorn is stored. This means that storing the popcorn in the refrigerator is the variable. A variable is the condition that is allowed to change.

There are two important things you need to know when you are setting up an experimental group. First you must know exactly what variable you are going to be testing. Then you must know how you are going to measure the results from the experimental group. In order to measure the results you must have some way of making a comparison. Comparing the results from the experimental group with the results of the control group is one way to measure the results you obtain from the experimental group.

Think about how the results of the popcorn experiment were measured. You measured the amount of popcorn that popped in each bag to see which bag produced more. Let's say that the control group produced 4 cups of popcorn and the experimental group produced 5 cups of popcorn. What conclusion could you make from this information?

In order for you to know exactly what causes a difference in the results between groups, only one variable can be measured at a time. For this reason it is important that you only test one variable in the experimental group. If you tried to test more than one variable, you would not be able to tell which one was responsible for any differences that occurred.

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