Almost all experimental studies are designed to include a control group and one or more experimental groups, each serving a different purpose. In most cases, participants are randomly assigned to either a control or experimental group.
Experimental groups are usually manipulated to try and change the out come of the experiment. Control groups are usually kept as natural or unchanged to provide a normal outcome for comparison in the experiment. Read the article to learn more about the two.
Experimental Group
The experimental group, is the group of subjects or participants that receives the experimental treatment, intervention or condition being studied. In other words, it is a group of items, animals or people being tested, which have one variable or condition changed from the other groups in the experiment. The variable is usually stated in the hypothesis and is the main focus of the experiment.
Experimental group is exposed to changes in the independent variable being tested. The values of the independent variable and the impact on the dependent variable are recorded. An experiment may include multiple experimental groups at one time.
Researchers will compare the responses of the experimental group to those of a control group to see if the independent variable impacted the participants.
An experiment must have at least one control group and one experimental group; however, a single experiment can include multiple experimental groups, which are all compared against the control group.
Having multiple experimental groups enables researchers to vary different levels of an experimental variable and compare the effects of these changes to the control group and among each other.
An example of an experimental group would be if someone wanted to see if music helps people sleep longer. The experimental population could be divided into two groups. One group would track the length of time they sleep each night without music playing. The other group would track the length of time they sleep each night when listening to music. This group would be your experimental group because something has been changed in this group. Listening to music while they sleep. This group is being “experimented” on.
What you need to know about Control Group
- Members of the experimental group are exposed to the experimental treatment, which is the variable or condition that the study aims to test. This treatment could be a drug, therapy, educational program, or any other factor under investigation.
- To ensure fairness and minimize bias, subjects are often randomly assigned to either the experimental group or the control group. Randomization helps create comparable groups, ensuring that the results are not skewed by pre-existing differences between the participants.
- Experimental groups can also be single-blind or double-blind. In single-blind studies, participants do not know whether they are in the experimental or control group. In double-blind studies, both participants and researchers are unaware of group assignments to reduce bias.
- While the experimental group is exposed to the treatment, efforts are made to control or account for confounding variables—factors other than the treatment that could influence the results.
- In clinical trials, the experimental group receives the investigational drug or treatment, while the control group may receive a placebo or the current standard of care.
Control Group
A control group is a fundamental component of experimental research design, and its primary purpose is to serve as a baseline or reference group against which the experimental group is compared. In other words, it is is a collection of factors that remain constant throughout an experiment.
The control group allows researchers to assess the natural course or behavior of the subjects in the absence of the experimental intervention. This baseline comparison helps determine whether any observed changes in the experimental group can be attributed to the treatment or are simply a result of the normal variation or other factors.
While all experiments have an experimental group, not all experiments require a control group. Controls are extremely useful where the experimental conditions are complex and difficult to isolate. Experiments that use control groups are called controlled experiments.
Unlike the experimental group, the control group is not exposed to the independent variable under investigation. So, it provides a baseline against which any changes in the experimental group can be compared.
In comparative experiments, members of a control group receive a standard treatment, a placebo, or no treatment at all. There may be more than one treatment group, more than one control group, or both.
A simple example of a controlled experiment may be used to determine whether or not plants need to be watered to live. The control group would be plants that are not watered. The experimental group would consist of plants that receive water. A clever scientist would wonder whether too much watering might kill the plants and would set up several experimental groups, each receiving a different amount of water.
Types of control groups
Positive and negative controls are two other types of control groups:
- Positive control groups are control groups in which the conditions guarantee a positive result. Positive control groups are effective to show the experiment is functioning as planned.
- Negative control groups are control groups in which conditions produce a negative outcome. Negative control groups help identify outside influences which may be present that were not unaccounted for, such as contaminants.
What you need to know about Control Group
- Members of the control group do not receive the experimental treatment, intervention, or condition. Instead, they may receive a placebo (inactive treatment) or no treatment at all, depending on the study design.
- In many experiments, subjects are randomly assigned to either the control group or the experimental group. Randomization helps ensure that the groups are comparable and that any differences between them are not due to pre-existing biases.
- Control groups can be single-blind or double-blind. In a single-blind design, the subjects do not know whether they are in the control or experimental group. In a double-blind design, both the subjects and the researchers are unaware of group assignments, reducing the potential for bias.
- Control groups are important in controlling or minimizing the influence of confounding variables—factors other than the treatment that could affect the study’s outcome.
- In some cases, control groups may receive a placebo or no treatment, which is ethically acceptable when there is no known effective treatment or when withholding treatment does not harm the subjects.
- In psychology studies, the experimental group might be exposed to a specific psychological intervention, such as cognitive-behavioral therapy, while the control group receives no treatment or an alternative treatment.
- In psychology experiments, control groups might be exposed to a neutral condition or a placebo, while the experimental group is exposed to the variable being studied.
Control vs Experimental Group: Key Differences
| Aspect | Control Group | Experimental Group |
|---|---|---|
| Purpose | Serves as a baseline or reference group. | Receives the experimental treatment or condition. |
| Treatment | Does not receive the experimental treatment. | Receives the experimental treatment or condition. |
| Randomization | Subjects may be randomly assigned to this group. | Subjects are randomly assigned to this group. |
| Blinding | Can be single-blind or double-blind. | Can be single-blind or double-blind. |
| Data Collection | Provides baseline data for comparison. | Data collected to assess the treatment’s effects. |
| Psychology experiments | Control groups might be exposed to a neutral condition or a placebo. | Experimental group is exposed to the variable being studied. |
Control vs Experimental Group: Key Takeaways
Purpose
- Control Group: It serves as a baseline or reference group against which the experimental group is compared. It does not receive the experimental treatment or intervention.
- Experimental Group: It is the group that receives the experimental treatment, intervention, or condition being studied.
Treatment
- Control Group: Receives no treatment or a placebo (inactive treatment) to ensure that any observed effects in the experimental group are due to the experimental treatment and not other factors.
- Experimental Group: Receives the treatment or intervention being studied.
Variables
- Control Group: Helps identify the natural course or behavior of the subjects without the experimental intervention.
- Experimental Group: Allows researchers to assess the effects of the experimental treatment or condition on the subjects.
Comparison
- Control Group: Used for comparison to determine whether the experimental treatment has an effect.
- Experimental Group: Used to measure the impact of the experimental treatment.
Randomization
- Control Group: Subjects in the control group may be randomly assigned, but they do not receive the experimental treatment.
- Experimental Group: Subjects are randomly assigned to ensure that the groups are comparable, with one group receiving the experimental treatment.
Outcome Measurement
- Control Group: Provides a basis for assessing the baseline or natural outcome in the absence of the experimental treatment.
- Experimental Group: Allows researchers to measure the treatment’s effects on the subjects.
Blinding
- Control Group: Can be single-blind or double-blind, where the subjects or researchers may not know who is in the control group.
- Experimental Group: Can also be single-blind or double-blind, depending on the study design.
Hypothesis Testing
- Control Group: Used to test whether the experimental group’s results significantly differ from the control group, supporting or refuting the research hypothesis.
- Experimental Group: The focus of hypothesis testing to determine if the treatment has a statistically significant effect.
Statistical Analysis
- Control Group: Data from the control group are used as a reference point in statistical comparisons.
- Experimental Group: Data from the experimental group are analyzed to evaluate the treatment’s effectiveness.
Validity
- Control Group: Ensures the internal validity of the experiment by controlling for confounding variables.
- Experimental Group: The group of interest for studying the research question and establishing causal relationships.