The Purpose and Examples of a Control Group

Amanda Robb, Lisa Roundy
  • Author
    Amanda Robb

    Amanda has taught high school science for over 10 years. She has a Master's Degree in Cellular and Molecular Physiology from Tufts Medical School and a Master's of Teaching from Simmons College. She is also certified in secondary special education, biology, and physics in Massachusetts.

  • Instructor
    Lisa Roundy

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

Learn what a control group is and why it is important. See the different types of control groups and their characteristics and find control group examples. Updated: 12/02/2021

What is a Control Group

What is the control group in an experiment? The control group definition is a group that does not include any change to the variable being tested. Why is a control important in an experiment? The control group is important because it acts as a benchmark to compare the results of the experiment to. The experimental group is the group that the scientist is testing. The experimental group experiences a change to a variable, or the conditions allowed to change in the experiment.

Types of Control Groups

There are two main types of control groups:

  • Positive control groups
  • Negative control groups

The positive control group is a group that is designed to produce the effect you are looking for in the experimental group. The positive control group shows the scientists that the desired results are possible. This helps prevent false negative results in the experimental group, where a negative result is obtained but is due to a failure in the experiment rather than a truly negative result based on the experimental conditions. Let's look at an example.

Say you wanted to test a mystery solution for the presence of proteins using a solution called Biuret. This solution turns purple in the presence of protein and is normally blue. In this experiment, you would also need a positive control group which you know contains protein. You would expect the positive control group to turn purple upon mixing with the Biuret reagent. This would tell you that the Biuret solution you have is working and that any negative result in the experimental group is due to the absence of protein and not a problem with the reagent.

A negative control group is a group that is not exposed to the variable the scientist is testing, called the independent variable. A negative control group serves as a benchmark to ensure that the results that are obtained are actually due to the independent variable and not anything else. An example of a negative control group is the group that receives a placebo in clinical trials. In a clinical trial for drug development, one group of patients gets the drug in question and the other group gets a pill that contains only inactive ingredients and no drug. This way, any effects seen in the experimental group can be attributed to the drug and not any other variables, such as the process of taking the medicine.

The table below compares the two types of control groups:

Characteristic Positive Control Group Negative Control Group
Definition A group that produces the expected result in the experimental group A group that does not receive any changes to the independent variable
Purpose To confirm the experimental procedures are working as expected To create a benchmark to compare the experimental results to
Example A sample is tested with a known chemical makeup to ensure a reagent is working correctly A patient group does not receive the drug treatment and instead is given a placebo

Why is a Control Group Important

The purpose of the control group is to create a benchmark to compare the experimental results to. It allows for study of the effects of the independent variable alone without confounding conditions. During an experiment, a scientist must consider what their independent variable is and what is being tested. Then, a negative control group should be created so the results can be compared.

What Is a Control Group?

Imagine that you want to know if salt makes water boil faster. You would want to heat one pan of water without salt and one pan of water with salt at the same temperature. Then you would compare how long it takes each pan of water to boil. In this experiment, the water without salt is your control group.

A control group is the group in a study that does not include the thing being tested and is used as a benchmark to measure the results of the other group.

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Importance of Control Groups

There must be at least two groups in any valid experiment: the experimental group and the control group. The experimental group is the group in which you are testing something. For the experiment described earlier, the pan of water with salt added is the experimental group. The only difference between the two groups is the addition of the salt. This means that salt is the variable. A variable is the condition that is allowed to change.

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. You would compare the results from the experimental group with the results of the control group to see what happens when you change the variable you want to examine. A control group is an essential part of an experiment because it allows you to eliminate and isolate these variables.

Control groups are particularly important in social sciences, such as psychology. This is because it is practically impossible to completely eliminate all of the bias and outside influence that could alter the results of the experiment, but control groups can be used to focus on the variable you're trying to test. Failure to provide evidence of strong control groups can cause a study to be considered invalid.

Types of Control Groups

There are two main types of control groups: positive control groups and negative control groups.

Positive Control Groups

In a positive control group, the control group is designed to produce the effect you are trying to reproduce in the experimental group.

This type of control group allows you to show that the desired result is possible in the experiment. In this situation, you would use something that is known to produce the desired result as the control group. This proves that the experimental conditions are valid. If the control group also fails, it would show that something is wrong with the conditions of the experiment. Positive control groups reduce the chance of a false negative. A false negative is a result that appears negative when it should not.

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Video Transcript

What Is a Control Group?

Imagine that you want to know if salt makes water boil faster. You would want to heat one pan of water without salt and one pan of water with salt at the same temperature. Then you would compare how long it takes each pan of water to boil. In this experiment, the water without salt is your control group.

A control group is the group in a study that does not include the thing being tested and is used as a benchmark to measure the results of the other group.

Importance of Control Groups

There must be at least two groups in any valid experiment: the experimental group and the control group. The experimental group is the group in which you are testing something. For the experiment described earlier, the pan of water with salt added is the experimental group. The only difference between the two groups is the addition of the salt. This means that salt is the variable. A variable is the condition that is allowed to change.

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. You would compare the results from the experimental group with the results of the control group to see what happens when you change the variable you want to examine. A control group is an essential part of an experiment because it allows you to eliminate and isolate these variables.

Control groups are particularly important in social sciences, such as psychology. This is because it is practically impossible to completely eliminate all of the bias and outside influence that could alter the results of the experiment, but control groups can be used to focus on the variable you're trying to test. Failure to provide evidence of strong control groups can cause a study to be considered invalid.

Types of Control Groups

There are two main types of control groups: positive control groups and negative control groups.

Positive Control Groups

In a positive control group, the control group is designed to produce the effect you are trying to reproduce in the experimental group.

This type of control group allows you to show that the desired result is possible in the experiment. In this situation, you would use something that is known to produce the desired result as the control group. This proves that the experimental conditions are valid. If the control group also fails, it would show that something is wrong with the conditions of the experiment. Positive control groups reduce the chance of a false negative. A false negative is a result that appears negative when it should not.

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Frequently Asked Questions

What is the control group of an experiment?

The control group of an experiment is a group that is not exposed to the independent variable and thus serves as a benchmark for which to compare the results of the experimental group to.

What is an example of a control group?

An example of a control group is a group of individuals in a clinical trial that receive placebo pills instead of medication.

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