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Scientific experiments often include two groups: the experimental group and the control group . Here's a closer look at the experimental group and how to distinguish it from the experimental group.

Key Takeaways: Experimental Group

• The experimental group is the set of subjects exposed to a change in the independent variable. While it's technically possible to have a single subject for an experimental group, the statistical validity of the experiment will be vastly improved by increasing the sample size.
• In contrast, the control group is identical in every way to the experimental group, except the independent variable is held constant. It's best to have a large sample size for the control group, too.
• It's possible for an experiment to contain more than one experimental group. However, in the cleanest experiments, only one variable is changed.

Experimental Group Definition

An experimental group in a scientific experiment is the group on which the experimental procedure is performed. The independent variable is changed for the group and the response or change in the dependent variable is recorded. In contrast, the group that does not receive the treatment or in which the independent variable is held constant is called the control group .

The purpose of having experimental and control groups is to have sufficient data to be reasonably sure the relationship between the independent and dependent variable is not due to chance. If you perform an experiment on only one subject (with and without treatment) or on one experimental subject and one control subject you have limited confidence in the outcome. The larger the sample size, the more probable the results represent a real correlation .

Example of an Experimental Group

You may be asked to identify the experimental group in an experiment as well as the control group. Here's an example of an experiment and how to tell these two key groups apart .

Let's say you want to see whether a nutritional supplement helps people lose weight. You want to design an experiment to test the effect. A poor experiment would be to take a supplement and see whether or not you lose weight. Why is it bad? You only have one data point! If you lose weight, it could be due to some other factor. A better experiment (though still pretty bad) would be to take the supplement, see if you lose weight, stop taking the supplement and see if the weight loss stops, then take it again and see if weight loss resumes. In this "experiment" you are the control group when you are not taking the supplement and the experimental group when you are taking it.

It's a terrible experiment for a number of reasons. One problem is that the same subject is being used as both the control group and the experimental group. You don't know, when you stop taking treatment, that is doesn't have a lasting effect. A solution is to design an experiment with truly separate control and experimental groups.

If you have a group of people who take the supplement and a group of people who do not, the ones exposed to the treatment (taking the supplement) are the experimental group. The ones not-taking it are the control group.

How to Tell Control and Experimental Group Apart

In an ideal situation, every factor that affects a member of both the control group and experimental group is exactly the same except for one -- the independent variable . In a basic experiment, this could be whether something is present or not. Present = experimental; absent = control.

Sometimes, it's more complicated and the control is "normal" and the experimental group is "not normal". For example, if you want to see whether or not darkness has an effect on plant growth. Your control group might be plants grown under ordinary day/night conditions. You could have a couple of experimental groups. One set of plants might be exposed to perpetual daylight, while another might be exposed to perpetual darkness. Here, any group where the variable is changed from normal is an experimental group. Both the all-light and all-dark groups are types of experimental groups.

Bailey, R.A. (2008). Design of Comparative Experiments . Cambridge: Cambridge University Press. ISBN 9780521683579.

Hinkelmann, Klaus and Kempthorne, Oscar (2008). Design and Analysis of Experiments, Volume I: Introduction to Experimental Design (Second ed.). Wiley. ISBN 978-0-471-72756-9.

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Experimental Group – Definition, Importance, Examples

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What is Experimental Group?

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• In the realm of scientific research, particularly within comparative experiments, the term “experimental group” is of paramount significance. This group, also referred to as the treatment group, is subjected to specific changes in a variable to observe potential reactions or outcomes. Such experiments may encompass multiple experimental groups, with each one exposed to varying degrees or levels of the said variable. This systematic variation facilitates a comprehensive understanding of the effects of different magnitudes of a variable on comparable subjects.
• Contrastingly, there exists a control group , which serves as a benchmark. The control group either remains unexposed or is exposed to a standardized level of the variable. This group’s primary function is to elucidate the inherent effects of the variable, offering a comparative baseline against which the outcomes of the experimental groups can be evaluated.
• In the context of biological research, where living organisms often form the subjects of study, the genetic homogeneity of these subjects becomes crucial. The rationale behind this is the intricate interplay between genetics and environmental factors. When organisms with distinct genetic backgrounds are exposed to a consistent variable, the outcomes might be influenced more by their genetic differences than by the variable itself. Such genetic variability can potentially skew results, making them less reliable or harder to interpret.
• To circumvent these challenges, especially in the domain of pharmaceutical research, drugs intended for human use undergo rigorous testing across a spectrum of animals. This phased approach, involving multiple experimental groups, enables researchers to discern the drug’s effects across varied genetic backgrounds. By progressively narrowing down the test subjects to those genetically closer to humans, the transition to human trials becomes more informed, minimizing unforeseen risks to the initial human recipients.
• In conclusion, the experimental group stands as a cornerstone in scientific experiments, enabling researchers to meticulously gauge the effects of variables. Ensuring genetic consistency among subjects, especially in biological studies, is pivotal to derive accurate, reliable, and generalizable results.

The experimental group, in scientific research, refers to the group subjected to specific changes or treatments in a variable to observe and evaluate potential outcomes, in contrast to a control group which remains unaltered or standardized for comparison.

In the context of scientific research, an experimental group functions as the primary subject of investigation to determine the effects of a specific variable or treatment. Here’s a step-by-step breakdown of how it operates:

• Selection: Researchers select participants or subjects for the study. These subjects are then randomly assigned to either the experimental group or the control group to ensure that each group is comparable at the outset.
• Manipulation: The experimental group receives the treatment or intervention that researchers want to study. This could be a new drug, a specific teaching method, a particular stimulus, or any other factor that the study aims to investigate.
• Control: While the experimental group undergoes the treatment, a control group is maintained under standard conditions without the treatment. This group serves as a baseline for comparison to determine the effects of the treatment.
• Measurement: After the treatment is administered, researchers measure specific outcomes in both the experimental and control groups. This could involve tests, observations, surveys, or any other data collection method relevant to the study.
• Comparison: The results from the experimental group are compared to those from the control group. Any significant differences in outcomes can be attributed to the treatment, assuming all other variables are held constant.
• Analysis: Researchers analyze the data to determine if the treatment had a statistically significant effect. This involves various statistical tests and methods to ensure the validity of the results.
• Conclusion: Based on the comparison and analysis, researchers draw conclusions about the efficacy or impact of the treatment. They determine whether the treatment had the desired effect, no effect, or an adverse effect.

In essence, the experimental group serves as the primary focus of investigation in experimental research. By comparing its outcomes with a control group, researchers can isolate the effects of the treatment or intervention, thereby providing insights into cause-and-effect relationships.

The use of an experimental group in scientific research offers several advantages, which contribute to the robustness and validity of experimental findings. Here are the primary advantages of employing an experimental group:

• Causality Determination: One of the most significant advantages of using an experimental group is the ability to establish cause-and-effect relationships. By manipulating a specific variable in the experimental group and observing the outcomes, researchers can infer whether changes in one variable lead to changes in another.
• Controlled Environment: Experimental groups allow researchers to control extraneous variables that might influence the outcome. This control ensures that any observed effects can be attributed to the manipulated variable rather than other confounding factors.
• Replicability: A well-defined experimental group allows for the replication of the study. Replicability is crucial in science as it ensures that findings are consistent across different settings and can be validated by other researchers.
• Precision: Experimental designs, by their nature, allow for precise measurements and interventions. This precision can lead to more accurate and detailed findings, enhancing the study’s overall quality.
• Flexibility: Researchers can modify the conditions or treatments within the experimental group to study various aspects of a phenomenon. This flexibility can lead to a deeper understanding of the subject matter.
• Random Assignment: In many experimental designs, participants are randomly assigned to either the experimental or control group. This randomization helps ensure that the groups are comparable at the outset, reducing the likelihood of selection bias.
• Generalizability: If the experimental group is chosen with a diverse set of participants or subjects, and the results are consistent, the findings can often be generalized to a broader population .
• Objective Analysis: Experimental designs, with their structured approach and reliance on statistical methods, allow for objective analysis of data, minimizing subjective biases.
• Ethical Considerations: In some cases, using an experimental group can be more ethical than other research methods. For instance, if a potential treatment shows promise, it might be unethical not to provide it to participants, which can be facilitated in an experimental design.
• Practical Implications: Findings derived from experimental groups can have real-world applications. For instance, in medical research, the effects of a new drug on an experimental group can inform treatment protocols and guidelines.

In summary, the use of an experimental group in research provides a structured and controlled environment that facilitates the exploration of cause-and-effect relationships, ensuring the rigor, validity, and reliability of the findings.

The use of an experimental group in scientific research is fundamental for understanding cause-and-effect relationships. However, there are inherent limitations associated with this approach. Here are the primary limitations of using an experimental group:

• External Validity Concerns: While experimental designs often ensure high internal validity, they may lack external validity. This means the results, although valid within the controlled environment of the experiment, might not be generalizable to broader populations or real-world settings.
• Ethical Constraints: Certain experimental manipulations can raise ethical issues. For instance, withholding a potentially beneficial treatment from a control group or exposing participants to harmful conditions might be deemed unethical.
• Artificial Conditions: The controlled and often sterile conditions of an experimental setting might not accurately represent real-world scenarios, leading to results that are not always applicable outside the laboratory.
• Resource Intensive: Experimental research can be costly and time-consuming, especially if it requires specialized equipment, facilities, or large sample sizes.
• Observer Effects: Participants’ knowledge that they are being observed or are part of an experiment (e.g., the Hawthorne Effect) can influence their behavior, potentially skewing results.
• Narrow Focus: Experimental research often zeroes in on specific variables, which might overlook the broader context or the interplay of multiple factors.
• Potential for Sample Bias: If the experimental group isn’t representative of the broader population, the results might not be generalizable. Even with random assignment, there’s a risk of unintentional biases.
• Manipulation Limitations: It might be impractical or impossible to manipulate certain variables in an experimental setting due to logistical or ethical constraints.
• Predominance of Quantitative Data: Experimental designs often emphasize quantitative data collection, which might miss out on qualitative insights or the subjective experiences of participants.
• Uncontrolled Variables: Despite best efforts, it’s challenging to control all potential confounding variables, especially in complex systems or human studies.
• Participant Reactivity: Participants might respond to the experimental setup or the act of being studied rather than the variable of interest, leading to misleading results.
• Reductionist Approach: Experimental methods often simplify complex phenomena to study them in isolation, which might not capture the full complexity or holistic nature of certain phenomena.

In summary, while experimental groups provide invaluable insights in scientific research, it’s crucial to recognize and account for these limitations when designing studies, interpreting results, and drawing conclusions.

The experimental group plays a fundamental role in scientific research, serving as the linchpin for empirical investigations. Its importance can be elucidated through the following points:

• Establishing Causality: The primary objective of many scientific experiments is to determine cause-and-effect relationships. By manipulating a specific variable in the experimental group and observing the outcomes, researchers can ascertain whether changes in one variable lead to changes in another.
• Comparative Analysis: The experimental group provides a basis for comparison against the control group. While the control group remains unaltered or is exposed to a baseline level of the variable, the experimental group undergoes specific treatments. This juxtaposition allows for a clearer understanding of the effects of the variable under study.
• Enhancing Validity: By focusing on the experimental group and ensuring that all other conditions remain constant, researchers can enhance the internal validity of their experiments. This ensures that observed effects can be attributed to the manipulated variable rather than extraneous factors.
• Facilitating Replicability: A well-defined experimental group allows other researchers to replicate the study, which is crucial for the validation and generalization of findings across different settings and populations.
• Enabling Controlled Manipulation: The experimental group offers researchers the flexibility to vary the levels or types of treatments, facilitating a deeper exploration of the variable’s effects. This can lead to nuanced insights, such as dose-response relationships or differential impacts based on treatment types.
• Advancing Scientific Knowledge: Through systematic experimentation with the experimental group, new theories can be proposed, existing hypotheses can be tested, and previous findings can be confirmed or refuted. This iterative process is foundational to the progression of scientific knowledge.
• Informing Policy and Practice: Findings derived from experimental groups can have practical implications. For instance, in medical research, the effects of a new drug on an experimental group can inform dosage recommendations, potential side effects, and therapeutic efficacy.

In summary, the experimental group is indispensable in the scientific method , providing a structured framework for investigating hypotheses and drawing informed conclusions. Its role in isolating and examining the effects of specific variables ensures the rigor and robustness of empirical research.

Examples of Experimental Group

In a structured experiment designed to investigate the potential impact of music on plant growth, plants were systematically categorized into distinct groups. The primary division comprised the control group, which was maintained in an environment devoid of music, and the experimental group. This experimental group was further subdivided, with each subset being exposed to a unique genre of music. To ensure the reliability of the results, it was imperative that the plants used were genetically identical, ideally clones, and that they exhibited homozygosity across all genes. This minimizes genetic variability, which could otherwise confound the results. By meticulously controlling external factors such as temperature and humidity, the experiment aimed to ascertain that any observed differences in growth patterns were solely attributable to the musical variations.

Ecosystems, with their intricate web of interactions, offer a rich platform for studying the effects of variables on a multitude of organisms simultaneously. One metric often employed to gauge ecosystem productivity is oxygen production, indicative of the prevalent algae quantity. In certain experimental designs, ecologists manipulate ecosystems by selectively adding or removing specific organisms. For instance, a river ecosystem might be artificially segmented into areas with and without aquatic insects using net barriers. In the unrestricted segment, insects not only consume algae but also contribute to the nutrient pool upon their demise, potentially promoting algal growth. By contrast, the netted segment, devoid of these insects, serves as the experimental group. Through measurements such as oxygen levels and other water quality indicators, researchers can draw inferences about the intricate interplay between various organism populations and their collective impact on the ecosystem.

In essence, these examples underscore the pivotal role of experimental groups in scientific research. By introducing specific changes or treatments to these groups and juxtaposing their outcomes against control groups, scientists can glean invaluable insights into the variables under investigation.

What is the primary purpose of an experimental group in scientific research? a) To serve as a baseline for comparison b) To undergo specific treatments or interventions c) To ensure the study has high external validity d) To replicate the results of previous studies

In an experimental design, which group remains unaltered or is exposed to a baseline level of the variable for comparison? a) Dependent group b) Independent group c) Experimental group d) Control group

Which of the following is a potential limitation of using an experimental group? a) High internal validity b) Lack of generalizability to real-world settings c) Ability to establish causality d) Precision in measurements

The Hawthorne Effect is associated with which phenomenon? a) Participants altering their behavior due to the experimental treatment b) Participants behaving differently because they know they are being observed c) Participants responding positively to any intervention d) Participants showing no change regardless of the intervention

Why is random assignment important in experimental research? a) To ensure high external validity b) To reduce the likelihood of selection bias c) To increase the sample size d) To ensure all participants receive the treatment

Which of the following best describes the control group in an experimental design? a) It undergoes the primary treatment or intervention. b) It is exposed to multiple variables simultaneously. c) It remains unexposed or is exposed to a standard level of the variable. d) It determines the external validity of the study.

In experimental research, what is the primary goal of controlling extraneous variables? a) To increase the complexity of the study b) To ensure that observed effects are due to the manipulated variable c) To reduce the sample size d) To enhance external validity

Which of the following is NOT a typical characteristic of an experimental group? a) Undergoing a specific treatment or intervention b) Serving as a benchmark for comparison c) Being observed for outcomes post-treatment d) Being randomly selected from the larger sample

Experimental groups are essential for: a) Qualitative research only b) Establishing correlational relationships c) Establishing cause-and-effect relationships d) Observational studies

Which of the following scenarios best exemplifies the use of an experimental group? a) Observing the natural behavior of animals in the wild b) Conducting a survey on people’s dietary habits c) Administering a new drug to a group of patients to test its efficacy d) Interviewing individuals about their life experiences

An experimental group refers to the group in a study that receives the treatment or intervention being tested. It is compared to a control group that does not receive the treatment to determine the treatment’s effects.

While the experimental group undergoes the treatment or intervention, the control group remains unaltered or is exposed to a baseline level of the variable. The control group serves as a benchmark for comparison.

Random assignment ensures that each participant has an equal chance of being placed in any group, reducing potential biases and ensuring that the groups are comparable at the outset.

Yes, a study can have multiple experimental groups if researchers are testing the effects of different levels or types of an intervention.

The primary purpose is to determine the effects of a specific treatment or intervention by comparing the outcomes of the experimental group to those of a control group.

Researchers control extraneous variables, use random assignment, and employ statistical tests to ensure that observed effects can be attributed to the treatment rather than other factors.

Some limitations include potential lack of external validity, ethical concerns, and the artificial nature of controlled conditions.

No, the experimental group can be exposed to any type of intervention, whether it’s believed to have positive, negative, or neutral effects.

Through techniques like random assignment, blinding (where participants or researchers don’t know who is receiving the treatment), and controlling extraneous variables.

Absolutely! Experimental groups are used in various fields, including psychology, education, economics, and social sciences, to test theories and interventions.

• Bailey, R. A. (2008). Design of Comparative Experiments. Cambridge University Press. ISBN 978-0-521-68357-9.
• Chaplin, S. (2006). “The placebo response: an important part of treatment”. Prescriber: 16–22. doi:10.1002/psb.344
• Hinkelmann, Klaus; Kempthorne, Oscar (2008). Design and Analysis of Experiments, Volume I: Introduction to Experimental Design (2nd ed.). Wiley. ISBN 978-0-471-72756-9.

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Control Group vs Experimental Group

Julia Simkus

Editor at Simply Psychology

BA (Hons) Psychology, Princeton University

Julia Simkus is a graduate of Princeton University with a Bachelor of Arts in Psychology. She is currently studying for a Master's Degree in Counseling for Mental Health and Wellness in September 2023. Julia's research has been published in peer reviewed journals.

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In a controlled experiment , scientists compare a control group, and an experimental group is identical in all respects except for one difference – experimental manipulation.

Differences

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.

Since experimental manipulation is the only difference between the experimental and control groups, we can be sure that any differences between the two are due to experimental manipulation rather than chance.

Almost all experimental studies are designed to include a control group and one or more experimental groups. In most cases, participants are randomly assigned to either a control or experimental group.

Because participants are randomly assigned to either group, we can assume that the groups are identical except for manipulating the independent variable in the experimental group.

It is important that every aspect of the experimental environment is the same and that the experimenters carry out the exact same procedures with both groups so researchers can confidently conclude that any differences between groups are actually due to the difference in treatments.

Control Group

A control group consists of participants who do not receive any experimental treatment. The control participants serve as a comparison group.

The control group is matched as closely as possible to the experimental group, including age, gender, social class, ethnicity, etc.

The difference between the control and experimental groups is that the control group is not exposed to the independent variable , which is thought to be the cause of the behavior being investigated.

Researchers will compare the individuals in the control group to those in the experimental group to isolate the independent variable and examine its impact.

The control group is important because it serves as a baseline, enabling researchers to see what impact changes to the independent variable produce and strengthening researchers’ ability to draw conclusions from a study.

Without the presence of a control group, a researcher cannot determine whether a particular treatment truly has an effect on an experimental group.

Control groups are critical to the scientific method as they help ensure the internal validity of a study.

Assume you want to test a new medication for ADHD . One group would receive the new medication, and the other group would receive a pill that looked exactly the same as the one that the others received, but it would be a placebo. The group that takes the placebo would be the control group.

Types of Control Groups

Positive control group.

• A positive control group is an experimental control that will produce a known response or the desired effect.
• A positive control is used to ensure a test’s success and confirm an experiment’s validity.
• For example, when testing for a new medication, an already commercially available medication could serve as the positive control.

Negative Control Group

• A negative control group is an experimental control that does not result in the desired outcome of the experiment.
• A negative control is used to ensure that there is no response to the treatment and help identify the influence of external factors on the test.
• An example of a negative control would be using a placebo when testing for a new medication.

Experimental Group

An experimental group consists of participants exposed to a particular manipulation of the independent variable. These are the participants who receive the treatment of interest.

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.

Assume you want to study to determine if listening to different types of music can help with focus while studying.

You randomly assign participants to one of three groups: one group that listens to music with lyrics, one group that listens to music without lyrics, and another group that listens to no music.

The group of participants listening to no music while studying is the control group, and the groups listening to music, whether with or without lyrics, are the two experimental groups.

Frequently Asked Questions

1. what is the difference between the control group and the experimental group in an experimental study.

Put simply; an experimental group is a group that receives the variable, or treatment, that the researchers are testing, whereas the control group does not. These two groups should be identical in all other aspects.

2. What is the purpose of a control group in an experiment

A control group is essential in experimental research because it:

Provides a baseline against which the effects of the manipulated variable (the independent variable) can be measured.

Helps to ensure that any changes observed in the experimental group are indeed due to the manipulation of the independent variable and not due to other extraneous or confounding factors.

Helps to account for the placebo effect, where participants’ beliefs about the treatment can influence their behavior or responses.

In essence, it increases the internal validity of the results and the confidence we can have in the conclusions.

3. Do experimental studies always need a control group?

Not all experiments require a control group, but a true “controlled experiment” does require at least one control group. For example, experiments that use a within-subjects design do not have a control group.

In  within-subjects designs , all participants experience every condition and are tested before and after being exposed to treatment.

These experimental designs tend to have weaker internal validity as it is more difficult for a researcher to be confident that the outcome was caused by the experimental treatment and not by a confounding variable.

4. Can a study include more than one control group?

Yes, studies can include multiple control groups. For example, if several distinct groups of subjects do not receive the treatment, these would be the control groups.

5. How is the control group treated differently from the experimental groups?

The control group and the experimental group(s) are treated identically except for one key difference: exposure to the independent variable, which is the factor being tested. The experimental group is subjected to the independent variable, whereas the control group is not.

This distinction allows researchers to measure the effect of the independent variable on the experimental group by comparing it to the control group, which serves as a baseline or standard.

Bailey, R. A. (2008). Design of Comparative Experiments. Cambridge University Press. ISBN 978-0-521-68357-9.

Hinkelmann, Klaus; Kempthorne, Oscar (2008). Design and Analysis of Experiments, Volume I: Introduction to Experimental Design (2nd ed.). Wiley. ISBN 978-0-471-72756-9.

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Experimental Group in Psychology Experiments

Kendra Cherry, MS, is a psychosocial rehabilitation specialist, psychology educator, and author of the "Everything Psychology Book."

Emily is a board-certified science editor who has worked with top digital publishing brands like Voices for Biodiversity, Study.com, GoodTherapy, Vox, and Verywell.

In a randomized and controlled psychology experiment , the researchers are examining the impact of an experimental condition on a group of participants (does the independent variable 'X' cause a change in the dependent variable 'Y'?). To determine cause and effect, there must be at least two groups to compare, the experimental group and the control group.

The participants who are in the experimental condition are those who receive the treatment or intervention of interest. The data from their outcomes are collected and compared to the data from a group that did not receive the experimental treatment. The control group may have received no treatment at all, or they may have received a placebo treatment or the standard treatment in current practice.

Comparing the experimental group to the control group allows researchers to see how much of an impact the intervention had on the participants.

A Closer Look at Experimental Groups

Imagine that you want to do an experiment to determine if listening to music while working out can lead to greater weight loss. After getting together a group of participants, you randomly assign them to one of three groups. One group listens to upbeat music while working out, one group listens to relaxing music, and the third group listens to no music at all. All of the participants work out for the same amount of time and the same number of days each week.

In this experiment, the group of participants listening to no music while working out is the control group. They serve as a baseline with which to compare the performance of the other two groups. The other two groups in the experiment are the experimental groups.   They each receive some level of the independent variable, which in this case is listening to music while working out.

In this experiment, you find that the participants who listened to upbeat music experienced the greatest weight loss result, largely because those who listened to this type of music exercised with greater intensity than those in the other two groups. By comparing the results from your experimental groups with the results of the control group, you can more clearly see the impact of the independent variable.  

Some Things to Know

When it comes to using experimental groups in a psychology experiment, there are a few important things to know:

• In order to determine the impact of an independent variable, it is important to have at least two different treatment conditions. This usually involves using a control group that receives no treatment against an experimental group that receives the treatment. However, there can also be a number of different experimental groups in the same experiment.
• Care must be taken when assigning participants to groups. So how do researchers determine who is in the control group and who is in the experimental group? In an ideal situation, the researchers would use random assignment to place participants in groups. In random assignment, each individual stands an equal shot at being assigned to either group. Participants might be randomly assigned using methods such as a coin flip or a number draw. By using random assignment, researchers can help ensure that the groups are not unfairly stacked with people who share characteristics that might unfairly skew the results.
• Variables must be well-defined. Before you begin manipulating things in an experiment, you need to have very clear operational definitions in place. These definitions clearly explain what your variables are, including exactly how you are manipulating the independent variable and exactly how you are measuring the outcomes.

A Word From Verywell

Experiments play an important role in the research process and allow psychologists to investigate cause-and-effect relationships between different variables. Having one or more experimental groups allows researchers to vary different levels or types of the experimental variable and then compare the effects of these changes against a control group. The goal of this experimental manipulation is to gain a better understanding of the different factors that may have an impact on how people think, feel, and act.

Byrd-Bredbenner C, Wu F, Spaccarotella K, Quick V, Martin-Biggers J, Zhang Y. Systematic review of control groups in nutrition education intervention research . Int J Behav Nutr Phys Act. 2017;14(1):91. doi:10.1186/s12966-017-0546-3

Steingrimsdottir HS, Arntzen E. On the utility of within-participant research design when working with patients with neurocognitive disorders . Clin Interv Aging. 2015;10:1189-1200. doi:10.2147/CIA.S81868

Oberste M, Hartig P, Bloch W, et al. Control group paradigms in studies investigating acute effects of exercise on cognitive performance—An experiment on expectation-driven placebo effects . Front Hum Neurosci. 2017;11:600. doi:10.3389/fnhum.2017.00600

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By Kendra Cherry, MSEd Kendra Cherry, MS, is a psychosocial rehabilitation specialist, psychology educator, and author of the "Everything Psychology Book."

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What are Experimental Groups in Research

The experimental group plays a key role in scientific studies, especially in psychology, medicine, and social sciences. In experimental research, this group helps in exploring cause-and-effect relationships and evaluating interventions or treatments. Understanding the importance, characteristics, and factors related to the experimental group is essential for accurate and reliable scientific studies.  

Table of Contents

What is an Experimental Group in Research ? (1)  

In research, an experimental group is a particular group of participants exposed to a treatment. Researchers use this group to observe and analyze the effects of the changed variable, called the independent variable.  

Control Group vs Experimental Group (2)  

Unlike the experimental group, the control group acts as a starting point. It experiences conditions similar to the experimental group but without exposure to the independent variable. Comparing these groups helps researchers understand the impact of the independent variable and establish cause-and-effect relationships in their studies.  

Example of Experimental Group (4)  

For instance, in a drug trial, the group trying the new medicine is the experimental group, and the group getting a fake treatment is the control group. In an educational study comparing teaching methods, the experimental group tries the new approach, while the control group sticks to the usual teaching method.  

Consider an experiment examining the impact of temperature on plant growth. The experimental group would be subjected to increased temperatures, while the control group experiences normal temperature conditions. This example illustrates the versatility of experimental groups across various research domains.  

Key Characteristics of Effective Experimental Groups in Research (1)  

• Random Assignment: Random assignment is when participants are chosen for the experimental or control group purely by chance. Random assignment makes the study more reliable by minimizing the impact of individual differences and enhancing the credibility of the research findings.  
• Homogeneity: Homogeneity ensures that people in the experimental group are similar to each other. When everyone in the experimental group is alike, it’s easier to link any changes to the treatment or intervention being studied, making the research results more reliable.  
• Isolation of Variables: In a scientific study, researchers change only one thing on purpose—the independent variable. This focused approach helps researchers connect any observed changes directly to that specific factor.   
• Replicability: A good experimental group is designed in a way that other researchers can do the same experiment to check or question the original findings. This ensures that the methods used in the study are clear and can be followed by others.   
• Data Collection: Information is gathered from the experimental group to understand specific outcomes or responses. It can involve different methods like surveys, observations, tests, or measurements, depending on the study’s design and goals. The collected data forms the basis for analysis and helps draw meaningful conclusions from the study.  

Advantages and Disadvantages of Experimental Groups in Research (1)(3)  

Advantages  

• Control Over Variables: Control over variables means that scientists deliberately focus on changing only one thing while keeping everything else constant. It ensures that changes in outcomes are likely due to the intentional changes made during the experiment.
• Precision: Precision means measuring the effects of an intervention very carefully, giving a clearer understanding of how it affects the study outcomes.  
• Comparative analysis: Comparative analysis involves comparing the group receiving an intervention (experimental group) with the group that doesn’t (control group). This comparison helps scientists see if and how the intervention is making a difference by carefully looking at the outcomes of both groups. Comparative analysis involves comparing the group receiving an intervention (experimental group) with the group that doesn’t (control group). This comparison helps scientists see if and how the intervention is making a difference by carefully looking at the outcomes of both groups.  

Disadvantages  

• Ethical Concerns: Ethical Concerns: Some experiments could be ethically problematic, especially when changing variables might harm those in the experimental group. Researchers must prioritize the well-being of participants in such cases.  
• External Validity: Findings from experimental groups might not apply to real-world situations, making the study less broadly applicable.  
• Time intensive: Engaging in experimental research demands a considerable investment of time, effort, and resources. This includes various activities such as recruiting participants, putting interventions into action, and gathering as well as analyzing data.  

Experimental groups in research are indispensable tools in science, providing a structured framework for investigating the impact of independent variables. By understanding the definition, examples, and key characteristics of experimental groups, researchers can conduct experiments that yield valuable insights. However, it is essential to acknowledge the advantages and disadvantages inherent in the use of experimental groups, ensuring a balanced and ethical approach to scientific inquiry.  

References:  

• The Role of Experimental Groups in Research – Mind the Graph Blog  
• The Difference Between Control Group and Experimental Group – ThoughtCo  
• Experimental & Control Group – Study.com  
• Experimental Group (Treatment Group): Definition, Examples – Statistics How To  

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Study guides for every class, that actually explain what's on your next test, experimental group, from class:.

An experimental group is a set of subjects in an experiment that receives the treatment or intervention being tested, allowing researchers to observe the effects of that treatment compared to a control group. This group is critical for establishing causal relationships because it provides a basis for comparison to evaluate the impact of the independent variable. Understanding the role of the experimental group helps in assessing the validity and reliability of experimental results.

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5 Must Know Facts For Your Next Test

• The experimental group is essential for determining the cause-and-effect relationship between variables in an experiment.
• Members of the experimental group receive the specific treatment, while the control group does not, highlighting differences in outcomes.
• It is important that all other conditions remain constant for both groups to ensure that any differences can be attributed solely to the treatment.
• Experimental groups can be utilized in various types of studies, including clinical trials, psychological experiments, and agricultural research.
• The size and composition of the experimental group can impact the reliability of results; larger groups often yield more accurate data.

Review Questions

• The experimental group plays a crucial role in establishing cause-and-effect relationships because it receives the treatment or intervention being tested. By comparing outcomes between the experimental group and a control group, researchers can determine if changes observed are due to the treatment itself rather than other factors. This comparison allows for conclusions about the effectiveness and impact of the independent variable on the dependent variable.
• Random assignment is vital for enhancing the validity of results from an experimental group as it ensures that each participant has an equal chance of being placed in either the experimental or control group. This process helps eliminate selection bias and ensures that both groups are similar in all respects except for the treatment. By balancing out any confounding variables, researchers can confidently attribute differences in outcomes to the treatment given to the experimental group.
• Variations in size or characteristics of an experimental group can significantly affect research conclusions by influencing statistical power and generalizability. A small experimental group may lead to unreliable results due to insufficient data to support claims, while a larger group can provide more robust findings. Additionally, if the characteristics of participants are not representative of the broader population, it may limit the applicability of findings. Thus, careful consideration must be given to both size and participant selection to ensure valid and applicable conclusions.

Related terms

A control group is a set of subjects that does not receive the treatment or intervention, serving as a baseline to compare against the experimental group.

Random assignment is a process used to assign subjects to experimental and control groups in a way that minimizes biases, ensuring that each participant has an equal chance of being placed in either group.

The independent variable is the factor that is manipulated or changed by researchers in an experiment to observe its effect on the dependent variable.

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