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Experimental Psychology

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The Simple Experiment: Two-group Design



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! 

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