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Explain why this study is classified as a between-subjects design. Additionally, explain how stable individual differences among the participants in the separate groups affect the within-groups variability () and the resulting statistic in the One-Way ANOVA.
Case context: A group of researchers wants to study the impact of defendant attractiveness on guilt judgments. They assign one group of participants to view an attractive defendant and another separate group to view an unattractive defendant. Each participant judges the guilt of the defendant they were shown. In their statistical analysis, the researchers plan to use a One-Way ANOVA to compare the means of these groups, but they must consider the impact of stable individual differences.
Question: Explain why this study is classified as a between-subjects design. Additionally, explain how stable individual differences among the participants in the separate groups affect the within-groups variability () and the resulting statistic in the One-Way ANOVA.
Sample answer: This study is a between-subjects design because each participant is exposed to only a single level of the independent variable (either the attractive or the unattractive defendant condition) rather than both. Because the groups consist of separate individuals, stable individual differences among them add to the overall variability within the groups. This increases the value of the within-groups variance (), which in turn decreases the calculated value of the statistic.
Key points:
- Each participant is exposed to only a single level of the independent variable (attractive or unattractive defendant condition).
- Stable individual differences in a between-subjects design add to the variability within the groups.
- Increased variability within the groups increases the value of .
- An increase in decreases the value of the statistic.
Rubric: The student response must: 1. Explain that participants are only exposed to one condition (attractive or unattractive defendant), representing a between-subjects design. 2. Comprehend that stable individual differences among separate participants add to the variability within the groups. 3. Describe how this within-group variability increases the value of the within-groups mean square (). 4. State that an increased leads to a decreased value of the statistic.
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Research Methods in Psychology - 4th American Edition @ KPU
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Advantages of Between-Subjects Experiments
Independent-Samples t-Test
One-Way ANOVA
Within-Subjects Experiment
Matched-Groups Design
Examples of Between-Subjects Experiments
Example of Lack of Context in Between-Subjects Designs
Combining Between-Subjects and Within-Subjects Designs
Equivalent Groups
Nonequivalent Groups
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