Why are control groups needed in experimental research and how are they different from the experimental group?
|
Design of Experiments > Control Group The control group
(sometimes called a comparison group) is used in an experiment as a way to ensure that your experiment actually works. It’s a way to make sure that the treatment you are giving is causing the experimental results, and not something outside the experiment. An experiment is split into two groups: the experimental
group and the control group. The experimental group is given the experimental treatment and the control group is given either a standard treatment or nothing. For example, let’s say you wanted to know if Gatorade increased athletic performance. Your experimental group would be given the Gatorade and your control group would be given regular water. The conditions must be exactly the same for all members in the experiment. The only difference between members must be the item or
thing you are conducting the experiment to look at. Let’s say you wanted to know if a new fertilizer makes plants grow taller. You must ensure that the lighting, water supply, size of container and other important factors are held constant for every member in every group. The only thing that differs in this case is the type of fertilizer given to the plants. Control groups can be subdivided into the following types (see:
FDA): Which type of control group you use depends largely on what type of patients you are administering a treatment too.
In many cases, it would be unethical to withhold treatment from a control group or provide a placebo. Next: The Placebo Effect. Beyer, W. H. CRC Standard Mathematical Tables, 31st ed. Boca Raton, FL: CRC Press, pp. 536 and 571, 2002.
--------------------------------------------------------------------------- Need help with a homework or test question? With Chegg Study, you can get step-by-step solutions to your questions from an expert in the field. Your first 30 minutes with a Chegg tutor is free! Comments? Need to post a correction? Please Contact Us. A control group in an experiment does not receive the treatment. Instead, it serves as a comparison group for the treatments. Researchers compare the results of a treatment group to the control group to determine the effect size, also known as the treatment effect. Imagine that a treatment group receives a vaccine and it has an infection rate of 10%. By itself, you don’t know if that’s an improvement. However, if you also have an unvaccinated control group with an infection rate of 20%, you know the vaccine improved the outcome by 10 percentage points. By serving as a basis for comparison, the control group reveals the treatment’s effect. Related post: Effect Sizes in Statistics Using Control Groups in ExperimentsMost experiments include a control group and at least one treatment group. In an ideal experiment, the subjects in all groups start with the same overall characteristics except that those in the treatment groups receive a treatment. When the groups are otherwise equivalent before treatment begins, you can attribute differences after the experiment to the treatments. Randomized controlled trials (RCTs) assign subjects to the treatment and control groups randomly. This process helps ensure the groups are comparable when treatment begins. Consequently, treatment effects are the most likely cause for differences between groups at the end of the study. Statisticians consider RCTs to be the gold standard. To learn more about this process, read my post, Random Assignment in Experiments. Observational studies either can’t use randomized groups or don’t use them because they’re too costly or problematic. In these studies, the characteristics of the control group might be different from the treatment groups at the start of the study, making it difficult to estimate the treatment effect accurately at the end. Case-Control studies are a specific type of observational study that uses a control group. For these types of studies, analytical methods and design choices, such as regression analysis and matching, can help statistically mitigate confounding variables. Matching involves selecting participants with similar characteristics. For each participant in the treatment group, the researchers find a subject with comparable traits to include in the control group. To learn more about this type of study and matching, read my post, Observational Studies Explained. Control groups are key way to increase the internal validity of an experiment. To learn more, read my post about internal and external validity. Randomized versus non-randomized control groups are just several of the different types you can have. We’ll look at more kinds later! Related posts: When to Use Regression Analysis Example of a Control GroupSuppose we want to determine whether regular vitamin consumption affects the risk of dying. Our experiment has the following two experimental groups:
In this experiment, we randomly assign subjects to the two groups. Because we use random assignment, the two groups start with similar characteristics, including healthy habits, physical attributes, medical conditions, and other factors affecting the outcome. The intentional introduction of vitamin supplements in the treatment group is the only systematic difference between the groups. After the experiment is complete, we compare the death risk between the treatment and control groups. Because the groups started roughly equal, we can reasonably attribute differences in death risk at the end of the study to vitamin consumption. By having the control group as the basis of comparison, the effect of vitamin consumption becomes clear! Types of Control GroupsResearchers can use different types of control groups in their experiments. Earlier, you learned about the random versus non-random kinds, but there are other variations. You can use various types depending on your research goals, constraints, and ethical issues, among other things. Negative Control GroupThe group introduces a condition that the researchers expect won’t have an effect. This group typically receives no treatment. These experiments compare the effectiveness of the experimental treatment to no treatment. For example, in a vaccine study, a negative control group does not get the vaccine. Positive Control GroupPositive control groups typically receive a standard treatment that science has already proven effective. These groups serve as a benchmark for the performance of a conventional treatment. In this vein, experiments with positive control groups compare the effectiveness of a new treatment to a standard one. For example, an old blood pressure medicine can be the treatment in a positive control group, while the treatment group receives the new, experimental blood pressure medicine. The researchers want to determine whether the new treatment is better than the previous treatment. In these studies, subjects can still take the standard medication for their condition, a potentially critical ethics issue. Placebo Control GroupPlacebo control groups introduce a treatment lookalike that will not affect the outcome. Standard examples of placebos are sugar pills and saline solution injections instead of genuine medicine. The key is that the placebo looks like the actual treatment. Researchers use this approach when the recipients’ belief that they’re receiving the treatment might influence their outcomes. By using placebos, the experiment controls for these psychological benefits. The researchers want to determine whether the treatment performs better than the placebo effect. Blinded Control GroupsIf the subject’s awareness of their group assignment might affect their outcomes, the researchers can use a blinded experimental design that does not tell participants their group membership. Typically, blinded control groups will receive placebos, as described above. In a double-blinded control group, both subjects and researchers don’t know group assignments. Waitlist Control GroupWhen there is a waitlist to receive a new treatment, those on the waitlist can serve as a control group until they receive treatment. This type of design avoids ethical concerns about withholding a better treatment until the study finishes. This design can be a variation of a positive control group because the subjects might be using conventional medicines while on the waitlist. Historical Control GroupWhen historical data for a comparison group exists, it can serve as a control group for an experiment. The group doesn’t exist in the study, but the researchers compare the treatment group to the existing data. For example, the researchers might have infection rate data for unvaccinated individuals to compare to the infection rate among the vaccinated participants in their study. This approach allows everyone in the experiment to receive the new treatment. However, differences in place, time, and other circumstances can reduce the value of these comparisons. In other words, other factors might account for the apparent effects. Why do you need a control group and how is this group different from your experimental group?The treatment group (also called the experimental group) receives the treatment whose effect the researcher is interested in. The control group receives either no treatment, a standard treatment whose effect is already known, or a placebo (a fake treatment).
Why do you need a control group in experiment research?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.
What is the difference between the control group and the experimental groups in an experiment?What is the difference between a control group and an experimental group? An experimental group, also known as a treatment group, receives the treatment whose effect researchers wish to study, whereas a control group does not. They should be identical in all other ways.
What is the difference between the control group and the experimental group in an experimental study quizlet?An experimental group is the group in the experiment that receives the variable being tested. A control group does not receive the test variable.
|
