Design of Experiments > Experimental Group
What is an Experimental Group?
An experimental group, also called a treatment group, is a group that receives a specific treatment in an experiment.
The “group” consists of test subjects, such as people, animals, cells, or plats, while the “treatment” refers to the variable being studied. For instance, a human experimental group might receive a treatment of new medication, alternative counseling, or vitamin supplements. A plant treatment group could be given new fertilizer, increased sunlight, or distilled water.
Treatments are administered to subjects by level — a measure of the amount or magnitude. For example, if the experimental subjects were given 1mg, 5mg, 10mg of a medication, those amounts would be the three levels of the treatment [1].
The group not receiving the treatment is called the control group.
Treatment Group Examples
- You are testing to see if a new plant fertilizer increases sunflower size. You put 20 plants of the same height and strain into a location where all the plants get the same amount of water and sunlight. One half of the plants–the control group–get the regular fertilizer. The other half of the plants–the experimental group–get the fertilizer you are testing.
- You are testing to see if a new drug works for asthma. You divide 100 volunteers into two groups of 50. One group of 50 gets the drug; they are the experimental group. The other 50 people get a sugar pill (a placebo); they are the control group.
- You want to prove that covering meat prevents maggots from hatching. You put meat into two different jars: one with a lid and one left open. The jar with the lid is the experimental group; the jar left open is the control group. (This is the famous Redi experiment).
The only difference between the control group and the experimental group must be the hypothesis you are testing. In the first example above, the people must be of similar age, health status, socioeconomic background etc. That way you know that if the drug improves asthma for the experimental group, it’s not due to other factors like better health status or a younger age.
| Treatment group | Control group |
| Participants receive a new drug for depression. | Participants receive a placebo. |
| Participants receive a new educational intervention for math skills. | Participants receive the standard math curriculum. |
| Participants receive a new type of exercise program for weight loss. | Participants receive a standard diet and exercise program. |
| Participants receive a new type of intervention for smoking cessation. | Participants receive standard smoking cessation treatment. |
Treatment group vs. experimental group
In certain fields, the term “treatment group” is preferred over “experimental group.” These fields include:- Medicine: Medical research often refers to a group of patients receiving a new drug or treatment as the “treatment group,” while the control group is commonly called the “placebo group.”
- Psychology: In psychological research, the “treatment group” typically consists of participants who receive a new therapy or intervention, and the control group is frequently known as the “waitlist group.”
- Education: Educational research uses the term “treatment group” to describe a group of students receiving a new educational intervention, while the control group is often called the “standard group.”
Both “treatment group” and “experimental group” are often used interchangeably, with no definitive consensus on which term is more suitable. However, the term “treatment group” tends to be more common in some fields compared to others.
What is the purpose of the experimental group?
The purpose of the experimental group is to examine the impact of the independent variable. The independent variable is the factor being altered by the researcher, while the dependent variable is measured to determine its response to the independent variable.
The experimental group receives the independent variable, whereas the control group does not.
This enables the researcher to compare the dependent variable’s changes between the two groups to ascertain if the independent variable is responsible for the alterations.
For instance, assume a researcher wants to study a new drug’s effects on depression. Participants would be randomly assigned to either the experimental or control group. The experimental group would receive the new drug, while the control group would get a placebo. The researcher would then assess participants’ depression levels before and after treatment. If the experimental group’s depression levels decrease significantly more than the control group’s, the researcher could infer that the new drug effectively treats depression.
The experimental group plays an important role in experimental design, and it is necessary to ensure that it closely resembles the control group. This helps account for confounding variables, which are other factors that might also be causing changes in the dependent variable. By accounting for these variables, researchers can have greater confidence that the dependent variable’s changes are genuinely caused by the independent variable.
Difference between independent variable and experimental group
The independent variable is the aspect being altered by the researcher, while the experimental group consists of participants who receive the independent variable.
A primary distinction between the independent variable and the experimental group is that the former is a variable, whereas the latter is a group of individuals. The independent variable can be any factor that the researcher modifies, such as medication type, exercise amount, or stress level. Meanwhile, the experimental group comprises participants exposed to the independent variable.
Another contrast between the independent variable and the experimental group is that the researcher controls the independent variable, while participants are randomly assigned to the experimental group. By ensuring the independent variable is the sole difference between the experimental and control groups, the researcher maintains control. Random assignment to the experimental group guarantees that participants share similarities in aspects like age, gender, and other factors that could influence the experiment’s outcomes.
References
- Valerie J. Easton and John H. McColl Statistics Glossary v1.1