Question 1

What is a two-group experimental design and why is it used?

Accepted Answer

A two-group design is the simplest way to establish a cause-effect relationship between two variables. It consists of an experimental group that receives a treatment and a control group that does not. This design allows researchers to determine whether manipulating the independent variable is responsible for observed changes in the dependent variable by comparing outcomes between the two groups.

Question 2

How do independent and dependent variables differ in a two-group experiment?

Accepted Answer

The independent variable is the condition manipulated by the researcher to detect changes, while the dependent variable is the outcome measured as a result. In the attraction study, physical arousal (independent variable) is manipulated through exercise, and perceived attractiveness (dependent variable) is measured using a 7-point Likert Scale. Understanding this distinction is essential for designing experiments that test cause-and-effect relationships.

Question 3

What role does the control group play in a two-group design?

Accepted Answer

The control group serves as a baseline for comparison by receiving all conditions identical to the experimental group except for the key ingredient being tested. In the treadmill study, the control group walked at 3 miles per hour while the experimental group ran at 6 miles per hour. This ensures that any differences in outcomes result from the independent variable manipulation, not other factors.

Question 4

How should researchers obtain informed consent before conducting a two-group experiment?

Accepted Answer

Researchers must provide informed consent that gives participants a synopsis of the study, including any risks and benefits of participation, and clearly communicates that participants are free to quit at any time. This ethical requirement ensures participants understand what they are agreeing to and can make an informed decision about their involvement in the research.

Question 5

Why is random assignment important when organizing experimental and control groups?

Accepted Answer

Random assignment ensures that participants are placed into groups based solely on chance rather than researcher bias or participant characteristics. This prevents subconscious assumptions on the part of the researcher from influencing group composition, which could confound results. Random assignment strengthens the validity of cause-and-effect conclusions drawn from the experiment.

Question 6

What statistical test is used to analyze results from a two-group design?

Accepted Answer

A t-test for independent means is used to compare outcomes between the experimental and control groups. This statistical analysis determines whether differences in the dependent variable between groups are significant or due to chance. In the arousal and attraction study, the t-test revealed that high arousal participants rated pictures as significantly more attractive than low arousal participants.

Question 7

How can researchers control for confounding variables when designing experimental conditions?

Accepted Answer

Researchers must keep all conditions identical between experimental and control groups except for the independent variable being manipulated. In the attraction study, both groups used the same treadmill for the same duration; only speed differed. Controlling factors like participant demographics, picture characteristics (no piercings or tattoos, head only), and measurement scales ensures that observed effects result from the independent variable alone.

簡単な実験: 2 つのグループの設計

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