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Based on the concept of within-groups variance, diagnose which study design the researcher should choose to maximize statistical sensitivity, and explain how each design handles the participants' stable individual differences.
Case context: A researcher is designing a study to investigate the effects of three different levels of cognitive load on reaction times. They know that participants naturally have different baseline reaction times due to stable individual differences in their nervous systems and muscles. The researcher is deciding whether to use a between-subjects design or a repeated-measures design and wants to choose the design that maximizes statistical sensitivity by minimizing the impact of these individual differences on within-groups variance.
Question: Based on the concept of within-groups variance, diagnose which study design the researcher should choose to maximize statistical sensitivity, and explain how each design handles the participants' stable individual differences.
Sample answer: The researcher should choose a repeated-measures design. In a repeated-measures ANOVA, stable individual differences are measured and subtracted from the within-groups variance (), which decreases and increases the sensitivity of the test. In contrast, if a between-subjects design were chosen, these stable individual differences would add to the within-groups variance (), decreasing the -ratio and reducing the test's ability to detect an effect.
Key points:
- The researcher should choose a repeated-measures design.
- Stable individual differences in reaction times would add to the within-groups variance () in a between-subjects design.
- An increased within-groups variance () in a between-subjects design decreases the -ratio.
- Stable individual differences are measured and subtracted from the within-groups variance () in a repeated-measures design.
- Subtracting individual differences from decreases within-groups variance and increases statistical sensitivity.
Rubric: To receive full credit, the answer must: 1. Identify the repeated-measures design as the correct choice to maximize sensitivity. 2. Demonstrate comprehension of how stable individual differences add to the within-groups variance () in a between-subjects design and decrease the -ratio. 3. Demonstrate comprehension of how stable individual differences are measured and subtracted from the within-groups variance () in a repeated-measures design to increase sensitivity.
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Research Methods in Psychology - 4th American Edition @ KPU
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