Control Group Purpose & Examples | What is a Control Group? – Video & Lesson Transcript | Study.com

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.

Let’s imagine you want to test how well a new antibiotic works against a certain bacteria. In the control group, you would use an established antibiotic that you know works against the bacteria. In the experimental group, you would use the new antibiotic. If the samples of the new antibiotic are not effective and the control group is effective, you could conclude that the new antibiotic is not effective against those particular bacteria. If the control group is not effective, you would conclude that something else affected the outcome of the experiment, and it would need to be repeated.

Negative Control Groups

Negative control groups are used to make sure that outside factors are taken into account so you can measure the accuracy of the results of an experiment.

A negative control group uses a sample that is not expected to work. The measurements you take from this group set a baseline against which you measure the results of the experimental group. In other words, the control group measures the results that would occur without the test variable being introduced to the experimental group.

Imagine you are conducting a field study to find out if a new medication improves the symptoms of depression. The experimental group is given the new medication, and the control group is given a placebo. In this case, a placebo is a pill containing no medication that has no physical effect.

The results from each group are different. Since a control group is used, you know that the difference is because of the treatment. If more people report feeling less depressed in the experimental group, you can assume that the higher rate of improvement is due to the effects of the medication. You can also see how effective the medication appears to be because you can compare the experimental group to the control group.

Lesson Summary

Let’s review. 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 and is one of the two groups in any valid experiment. The experimental group is the other one and is the group in which you are testing something.

There are two types of 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. Negative control groups are used to make sure that outside factors are taken into account, so you can measure the accuracy of the results of an experiment.