two groups of experimental research

Experimental Research Designs: Types, Examples & Methods

Experimental research is the most familiar type of research design for individuals in the physical sciences and a host of other fields. This is mainly because experimental research is a classical scientific experiment, similar to those performed in high school science classes.

Imagine taking 2 samples of the same plant and exposing one of them to sunlight, while the other is kept away from sunlight. Let the plant exposed to sunlight be called sample A, while the latter is called sample B.

If after the duration of the research, we find out that sample A grows and sample B dies, even though they are both regularly wetted and given the same treatment. Therefore, we can conclude that sunlight will aid growth in all similar plants.

What is Experimental Research?

Experimental research is a scientific approach to research, where one or more independent variables are manipulated and applied to one or more dependent variables to measure their effect on the latter. The effect of the independent variables on the dependent variables is usually observed and recorded over some time, to aid researchers in drawing a reasonable conclusion regarding the relationship between these 2 variable types.

The experimental research method is widely used in physical and social sciences, psychology, and education. It is based on the comparison between two or more groups with a straightforward logic, which may, however, be difficult to execute.

Mostly related to a laboratory test procedure, experimental research designs involve collecting quantitative data and performing statistical analysis on them during research. Therefore, making it an example of quantitative research method .

What are The Types of Experimental Research Design?

The types of experimental research design are determined by the way the researcher assigns subjects to different conditions and groups. They are of 3 types, namely; pre-experimental, quasi-experimental, and true experimental research.

Pre-experimental Research Design

In pre-experimental research design, either a group or various dependent groups are observed for the effect of the application of an independent variable which is presumed to cause change. It is the simplest form of experimental research design and is treated with no control group.

Although very practical, experimental research is lacking in several areas of the true-experimental criteria. The pre-experimental research design is further divided into three types

One-shot Case Study Research Design

In this type of experimental study, only one dependent group or variable is considered. The study is carried out after some treatment which was presumed to cause change, making it a posttest study.

One-group Pretest-posttest Research Design:

This research design combines both posttest and pretest study by carrying out a test on a single group before the treatment is administered and after the treatment is administered. With the former being administered at the beginning of treatment and later at the end.

Static-group Comparison:

In a static-group comparison study, 2 or more groups are placed under observation, where only one of the groups is subjected to some treatment while the other groups are held static. All the groups are post-tested, and the observed differences between the groups are assumed to be a result of the treatment.

Quasi-experimental Research Design

The word “quasi” means partial, half, or pseudo. Therefore, the quasi-experimental research bearing a resemblance to the true experimental research, but not the same. In quasi-experiments, the participants are not randomly assigned, and as such, they are used in settings where randomization is difficult or impossible.

This is very common in educational research, where administrators are unwilling to allow the random selection of students for experimental samples.

Some examples of quasi-experimental research design include; the time series, no equivalent control group design, and the counterbalanced design.

True Experimental Research Design

The true experimental research design relies on statistical analysis to approve or disprove a hypothesis. It is the most accurate type of experimental design and may be carried out with or without a pretest on at least 2 randomly assigned dependent subjects.

The true experimental research design must contain a control group, a variable that can be manipulated by the researcher, and the distribution must be random. The classification of true experimental design include:

The posttest-only Control Group Design: In this design, subjects are randomly selected and assigned to the 2 groups (control and experimental), and only the experimental group is treated. After close observation, both groups are post-tested, and a conclusion is drawn from the difference between these groups.
The pretest-posttest Control Group Design: For this control group design, subjects are randomly assigned to the 2 groups, both are presented, but only the experimental group is treated. After close observation, both groups are post-tested to measure the degree of change in each group.
Solomon four-group Design: This is the combination of the pretest-only and the pretest-posttest control groups. In this case, the randomly selected subjects are placed into 4 groups.

The first two of these groups are tested using the posttest-only method, while the other two are tested using the pretest-posttest method.

Examples of Experimental Research

Experimental research examples are different, depending on the type of experimental research design that is being considered. The most basic example of experimental research is laboratory experiments, which may differ in nature depending on the subject of research.

Administering Exams After The End of Semester

During the semester, students in a class are lectured on particular courses and an exam is administered at the end of the semester. In this case, the students are the subjects or dependent variables while the lectures are the independent variables treated on the subjects.

Only one group of carefully selected subjects are considered in this research, making it a pre-experimental research design example. We will also notice that tests are only carried out at the end of the semester, and not at the beginning.

Further making it easy for us to conclude that it is a one-shot case study research.

Employee Skill Evaluation

Before employing a job seeker, organizations conduct tests that are used to screen out less qualified candidates from the pool of qualified applicants. This way, organizations can determine an employee’s skill set at the point of employment.

In the course of employment, organizations also carry out employee training to improve employee productivity and generally grow the organization. Further evaluation is carried out at the end of each training to test the impact of the training on employee skills, and test for improvement.

Here, the subject is the employee, while the treatment is the training conducted. This is a pretest-posttest control group experimental research example.

Evaluation of Teaching Method

Let us consider an academic institution that wants to evaluate the teaching method of 2 teachers to determine which is best. Imagine a case whereby the students assigned to each teacher is carefully selected probably due to personal request by parents or due to stubbornness and smartness.

This is a no equivalent group design example because the samples are not equal. By evaluating the effectiveness of each teacher’s teaching method this way, we may conclude after a post-test has been carried out.

However, this may be influenced by factors like the natural sweetness of a student. For example, a very smart student will grab more easily than his or her peers irrespective of the method of teaching.

What are the Characteristics of Experimental Research?

Experimental research contains dependent, independent and extraneous variables. The dependent variables are the variables being treated or manipulated and are sometimes called the subject of the research.

The independent variables are the experimental treatment being exerted on the dependent variables. Extraneous variables, on the other hand, are other factors affecting the experiment that may also contribute to the change.

The setting is where the experiment is carried out. Many experiments are carried out in the laboratory, where control can be exerted on the extraneous variables, thereby eliminating them.

Other experiments are carried out in a less controllable setting. The choice of setting used in research depends on the nature of the experiment being carried out.

Multivariable

Experimental research may include multiple independent variables, e.g. time, skills, test scores, etc.

Why Use Experimental Research Design?

Experimental research design can be majorly used in physical sciences, social sciences, education, and psychology. It is used to make predictions and draw conclusions on a subject matter.

Some uses of experimental research design are highlighted below.

Medicine: Experimental research is used to provide the proper treatment for diseases. In most cases, rather than directly using patients as the research subject, researchers take a sample of the bacteria from the patient’s body and are treated with the developed antibacterial

The changes observed during this period are recorded and evaluated to determine its effectiveness. This process can be carried out using different experimental research methods.

Education: Asides from science subjects like Chemistry and Physics which involves teaching students how to perform experimental research, it can also be used in improving the standard of an academic institution. This includes testing students’ knowledge on different topics, coming up with better teaching methods, and the implementation of other programs that will aid student learning.
Human Behavior: Social scientists are the ones who mostly use experimental research to test human behaviour. For example, consider 2 people randomly chosen to be the subject of the social interaction research where one person is placed in a room without human interaction for 1 year.

The other person is placed in a room with a few other people, enjoying human interaction. There will be a difference in their behaviour at the end of the experiment.

UI/UX: During the product development phase, one of the major aims of the product team is to create a great user experience with the product. Therefore, before launching the final product design, potential are brought in to interact with the product.

For example, when finding it difficult to choose how to position a button or feature on the app interface, a random sample of product testers are allowed to test the 2 samples and how the button positioning influences the user interaction is recorded.

What are the Disadvantages of Experimental Research?

It is highly prone to human error due to its dependency on variable control which may not be properly implemented. These errors could eliminate the validity of the experiment and the research being conducted.
Exerting control of extraneous variables may create unrealistic situations. Eliminating real-life variables will result in inaccurate conclusions. This may also result in researchers controlling the variables to suit his or her personal preferences.
It is a time-consuming process. So much time is spent on testing dependent variables and waiting for the effect of the manipulation of dependent variables to manifest.
It is expensive.
It is very risky and may have ethical complications that cannot be ignored. This is common in medical research, where failed trials may lead to a patient’s death or a deteriorating health condition.
Experimental research results are not descriptive.
Response bias can also be supplied by the subject of the conversation.
Human responses in experimental research can be difficult to measure.

What are the Data Collection Methods in Experimental Research?

Data collection methods in experimental research are the different ways in which data can be collected for experimental research. They are used in different cases, depending on the type of research being carried out.

1. Observational Study

This type of study is carried out over a long period. It measures and observes the variables of interest without changing existing conditions.

When researching the effect of social interaction on human behavior, the subjects who are placed in 2 different environments are observed throughout the research. No matter the kind of absurd behavior that is exhibited by the subject during this period, its condition will not be changed.

This may be a very risky thing to do in medical cases because it may lead to death or worse medical conditions.

2. Simulations

This procedure uses mathematical, physical, or computer models to replicate a real-life process or situation. It is frequently used when the actual situation is too expensive, dangerous, or impractical to replicate in real life.

This method is commonly used in engineering and operational research for learning purposes and sometimes as a tool to estimate possible outcomes of real research. Some common situation software are Simulink, MATLAB, and Simul8.

Not all kinds of experimental research can be carried out using simulation as a data collection tool . It is very impractical for a lot of laboratory-based research that involves chemical processes.

A survey is a tool used to gather relevant data about the characteristics of a population and is one of the most common data collection tools. A survey consists of a group of questions prepared by the researcher, to be answered by the research subject.

Surveys can be shared with the respondents both physically and electronically. When collecting data through surveys, the kind of data collected depends on the respondent, and researchers have limited control over it.

Formplus is the best tool for collecting experimental data using survey s. It has relevant features that will aid the data collection process and can also be used in other aspects of experimental research.

Differences between Experimental and Non-Experimental Research

1. In experimental research, the researcher can control and manipulate the environment of the research, including the predictor variable which can be changed. On the other hand, non-experimental research cannot be controlled or manipulated by the researcher at will.

This is because it takes place in a real-life setting, where extraneous variables cannot be eliminated. Therefore, it is more difficult to conclude non-experimental studies, even though they are much more flexible and allow for a greater range of study fields.

2. The relationship between cause and effect cannot be established in non-experimental research, while it can be established in experimental research. This may be because many extraneous variables also influence the changes in the research subject, making it difficult to point at a particular variable as the cause of a particular change

3. Independent variables are not introduced, withdrawn, or manipulated in non-experimental designs, but the same may not be said about experimental research.

Experimental Research vs. Alternatives and When to Use Them

1. experimental research vs causal comparative.

Experimental research enables you to control variables and identify how the independent variable affects the dependent variable. Causal-comparative find out the cause-and-effect relationship between the variables by comparing already existing groups that are affected differently by the independent variable.

For example, in an experiment to see how K-12 education affects children and teenager development. An experimental research would split the children into groups, some would get formal K-12 education, while others won’t. This is not ethically right because every child has the right to education. So, what we do instead would be to compare already existing groups of children who are getting formal education with those who due to some circumstances can not.

Pros and Cons of Experimental vs Causal-Comparative Research

Causal-Comparative: Strengths: More realistic than experiments, can be conducted in real-world settings. Weaknesses: Establishing causality can be weaker due to the lack of manipulation.

2. Experimental Research vs Correlational Research

When experimenting, you are trying to establish a cause-and-effect relationship between different variables. For example, you are trying to establish the effect of heat on water, the temperature keeps changing (independent variable) and you see how it affects the water (dependent variable).

For correlational research, you are not necessarily interested in the why or the cause-and-effect relationship between the variables, you are focusing on the relationship. Using the same water and temperature example, you are only interested in the fact that they change, you are not investigating which of the variables or other variables causes them to change.

Pros and Cons of Experimental vs Correlational Research

3. experimental research vs descriptive research.

With experimental research, you alter the independent variable to see how it affects the dependent variable, but with descriptive research you are simply studying the characteristics of the variable you are studying.

So, in an experiment to see how blown glass reacts to temperature, experimental research would keep altering the temperature to varying levels of high and low to see how it affects the dependent variable (glass). But descriptive research would investigate the glass properties.

Pros and Cons of Experimental vs Descriptive Research

4. experimental research vs action research.

Experimental research tests for causal relationships by focusing on one independent variable vs the dependent variable and keeps other variables constant. So, you are testing hypotheses and using the information from the research to contribute to knowledge.

However, with action research, you are using a real-world setting which means you are not controlling variables. You are also performing the research to solve actual problems and improve already established practices.

For example, if you are testing for how long commutes affect workers’ productivity. With experimental research, you would vary the length of commute to see how the time affects work. But with action research, you would account for other factors such as weather, commute route, nutrition, etc. Also, experimental research helps know the relationship between commute time and productivity, while action research helps you look for ways to improve productivity

Pros and Cons of Experimental vs Action Research

Conclusion .

Experimental research designs are often considered to be the standard in research designs. This is partly due to the common misconception that research is equivalent to scientific experiments—a component of experimental research design.

In this research design, one or more subjects or dependent variables are randomly assigned to different treatments (i.e. independent variables manipulated by the researcher) and the results are observed to conclude. One of the uniqueness of experimental research is in its ability to control the effect of extraneous variables.

Experimental research is suitable for research whose goal is to examine cause-effect relationships, e.g. explanatory research. It can be conducted in the laboratory or field settings, depending on the aim of the research that is being carried out.

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The Simple Experiment: Two-group Design

Previous video 2.4: perspectives on experimental psychology, next video 2.13: placebos in research, 63,502 views.

Source: Laboratories of Gary Lewandowski , Dave Strohmetz, and Natalie Ciarocco—Monmouth University

A two-group design is the simplest way to establish a cause-effect relationship between two variables. This video demonstrates a simple experiment (two-group design). In providing an overview of how a researcher conducts a simple experiment (two-group design), this video shows viewers the process of turning ideas into testable ideas and forming hypothesis, the identification and effect of experiment variables, the formation of experimental conditions and controls, the process of conducting the study, the collection of results, and the consideration their implications. This research technique is demonstration in the context of answering the research question: “How does physiological arousal/excitement influence perceived attraction?”

1. Introduction of topic/research question

Research question: All research seeks to answer questions. Often those questions start out fairly broad ( e.g. , What leads to attraction?). The researcher then forms a hypothesis based on educated guesses about potential answers.
Research hypothesis: Those who are experiencing high excitement will see others as more attractive than those who are experiencing low excitement.

2. Key variables

Variable = anything that changes in a study
Based on the hypothesis, excitement is the independent variable.
Based on the hypothesis, perceived attractiveness is the dependent variable.

3. Defining the variables

To manipulate the independent variable of excitement, have participants run on a treadmill.
To measure the dependent variable of perceived attractiveness, show participants pictures.

4. Establishing conditions

Ethical consideration: In using a manipulation that requires physical effort such as this, the researcher must be mindful of the pertinent ethical considerations ( i.e. , people should be in shape and cannot have them run too hard to too long)
Control condition = The condition that does not have the key ingredient. This group serves as the baseline for comparison.

5. Experimental control

What it is: Keeping everything exactly identical across conditions except for the key piece that the researcher wants to manipulate/change
It’s importance: This is the only way a researcher can isolate which piece or factor is responsible for the changes in the dependent variable.
Application to study: In the present study the researcher wants to focus on how excitement/arousal influences attraction. As such, excitement/arousal should be the only piece that changes between conditions. Thus, if the experimental group (high arousal) runs on a treadmill at 6mph for 3 minutes in a lab, the control group should be as similar as possible. They should be on a treadmill in lab for 3 minutes, but should walk at 3mph.

6. Measuring the dependent variable (attraction)

Key measurement considerations: shouldn’t be too attractive or unattractive, shouldn’t have piercings/tattoos; and should just be head shot
7-point Likert Scale: 1 = extremely unattractive; 7 = extremely attractive

7. Procedure/conducting the study

Tell participants: “Here is the informed consent, which outlines what the study is basically about, any risks/benefits of participation, and lets you know that you are free to quit at any time.”
Randomly order the packets so that the participant’s condition (running or walking) is not based on anything other than chance. Otherwise, the researcher may subconsciously be more likely to assign certain participants ( e.g. , those who look physically fit) to certain conditions ( e.g. , running).
Set treadmill to 6 mph, explain to the participant what they need to do, and start the timer for 3 min.
Show participants a series of pictures and ask them to rate on provided scale (1 = not at all attractive through 7 = extremely attractive).
Set treadmill to 3 mph, explain to the participant what they need to do, and start the timer for 3 min.
Explain the purpose of the study to the participant: “Thank you for participating. In this study I was trying to determine if excitement or arousal from exercise would lead participants to find a picture more attractive. To manipulate excitement/arousal there were two conditions; running vs. walking on the treadmill. Do you have any questions?”

Experimental design is the process by which a researcher plans a study. A two-group design is the simplest way to establish a cause-effect relationship between two variables.

Here, a two-group experimental design is used to answer the research question: “How does physiological arousal in the form of exercise influence perceived attraction? In other words, are people more attractive to you after a workout?”

This video demonstrates the process of turning concepts into testable ideas and forming hypotheses, how to design experimental conditions and controls as well as how to identify experimental variables, how to execute the study, and finally, analysis of the data and consideration of their implications.

All research seeks to answer questions. Often those questions start out fairly broad. The researcher then forms a hypothesis based on educated guesses about potential answers.

Here, the researcher forms the research hypothesis that those who are experiencing high excitement through exercise will see others as more attractive than those who are experiencing low excitement.

To test this hypothesis, the researcher organizes two groups of people: an experimental group and a control group. The experimental group is the one that receives the treatment, which in the case of today’s experiment is running on a treadmill. The treatment is the key ingredient that the researcher believes will influence the outcome.

The control group does not have the key ingredient. This group serves as the baseline for comparison. In the control group, everything must be kept exactly identical to the experimental group except for that key ingredient that the researcher wants to manipulate.

In the present study, the researcher wants to focus on how physical excitement influences attraction. As such, physical excitement should be the only piece that changes between experimental and control groups. Therefore, the control group will walk on the same treadmill for the same amount of time that the experimental group will run on the treadmill, in order to remove the excited state from the condition.

Now, consider the variables, which are things that change within the experiment. In a cause and effect scenario, the cause, or the condition manipulated to detect changes, is called the independent variable. The effect, or the outcome that the researcher measures, is called the dependent variable.

Based on the hypothesis, excitement is the independent variable and perceived attractiveness is the dependent variable.

As we’ve mentioned, in order to manipulate the independent variable of physical arousal, the experimental group will run on a treadmill.

Including a control group is the only way the researcher can determine if changing the independent variable is responsible for the observed changes in the dependent variable.

To measure the dependent variable of perceived attractiveness, participants in both groups will view pictures. It is important to consider factors that could complicate interpretation of the results. For example, in this case the subject in the picture shouldn’t have piercings or tattoos, and should only include the head.

Here, perceived attraction is quantified through use of the 7-point Likert Scale, where 1 is designated as “Extremely Unattractive” and 7 as “Extremely Attractive.” Now that the experimental design has been established, we can proceed to conducting the experiment.

To begin the experiment, the researcher needs to obtain the subject’s informed consent to participate in the study. The informed consent gives a synopsis of the study—any risks and benefits of participation—and lets the participant know that they are free to quit at any time.

Next, make random assignments to the groups, so that the participant’s group isn’t based on anything other than chance, and any subconscious assumptions on the part of the researcher are avoided.

To perform the experimental condition, bring the participant to the treadmill and explain to the participant what she needs to do. Then, allow the participant to set the treadmill to 6 miles per hour. When the participant begins, immediately start the timer for 3 min.

Afterwards, show the participant a series of pictures and ask her to rate on the provided scale.

For the control study, once again explain to the participant what she needs to do. Allow the participant to set the treadmill to 3 miles per hour, and start the timer for 3 min at the moment the participant begins.

The control subject then rates the attractiveness of the pictures in an identical manner to experimental group.

Following the experiment, give the subject a debriefing where the researcher explains the purpose of the study.

Researcher: Thank you for participating. In this study I was trying to determine if arousal from exercise would lead participants to find a picture of a person more attractive. To manipulate arousal there were two conditions: running vs. walking on the treadmill. Do you have any questions?

After collecting data from 122 people, a t-test was performed for independent means comparing the high arousal condition—achieved through running—to the low arousal condition—achieved through walking—to see how they influenced attraction.

The results reveal that those subjected to the high arousal condition found the pictures more attractive than those subjected to the low arousal condition.

The results of this study are similar to the famous “bridge study” performed by Donald Dutton and Arthur Aron in 1974. In this study, Dutton and Aron found that unaccompanied men who crossed a high shaky bridge were more likely to follow up with a female research assistant than other men who crossed a low sturdy bridge.

Now that you are familiar with setting up a simple experiment using two-group design, you can apply this approach to answer the specific questions of your research.

The two-group experimental design is commonly used in psychological experiments to determine a cause and effect relationship of the intervention in question.

For example, researchers used this type of experiment to determine the effectiveness of combined self-management and relaxation-breathing training for children with moderate-to-severe asthma.

In this study, the independent variable was the type of training provided to the children, and the dependent variables were made up of four physiological variables, including anxiety levels. The results revealed that a combination of self-management and relaxation-breathing training can reduce anxiety in asthmatic children.

In another study, the impact of a feeding log on breastfeeding duration and exclusivity was assessed. The experimental group completed a daily breastfeeding log while the control group did not. The log served to intervene with the participant in the self-regulation process.

The findings suggest that the breastfeeding log may be a valuable tool in self-regulating breastfeeding and promoting a longer duration of full breastfeeding.

You’ve just watched JoVE’s introduction on performing a simple experiment using two-group design. Now, you should have a good understanding of how to form a hypothesis, how to design experimental conditions and controls, as well as how to identify variables. You should also have a comprehension for how to perform a study, and how to assess the results.

And remember, considering the potential effects of arousal on attraction, a first date at the amusement park may be a better choice than a first date at a poetry reading.

Thanks for watching!

After collecting data from 122 people, a t-test for independent means was performed comparing the high arousal (running) condition to the low arousal (walking) condition to see how they influenced attraction. As shown in Figure 1 , those in the running/high arousal condition, depicted with the red bar found the pictures more attractive than those in the walking/low arousal condition.

The results of this study are similar to the famous “bridge study” where researchers found that men who crossed a high shaky bridge were more attracted to a female, than other men who crossed a low sturdy bridge. 1

Applications and Summary

Considering the potential effects of arousal on attraction, it may be better to talk to someone you’re interested in while at the gym, instead of the library. It also suggests that a rock concert may be better first date than a poetry reading.

Dutton, D. G., & Aron, A. P. Some evidence for heightened sexual attraction under conditions of high anxiety. Journal of Personality and Social Psychology. 30 (4), 510-517. doi:10.1037/h0037031 (1974).

As we’ve mentioned, in order to manipulate the independent variable of physical arousal, the experimental group will run on a treadmill.

Next, make random assignments to the groups, so that the participant’s group isn’t based on anything other than chance, and any subconscious assumptions on the part of the researcher are avoided.

Thanks for watching!