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Based on the design of this study, diagnose the group composition. Are the groups in this between-subjects experiment considered equivalent or nonequivalent? Justify your decision based on how the participants were placed into conditions.
Case context: A developmental psychologist wants to study the effect of a new interactive reading program on vocabulary retention. She recruits children from two local elementary schools. The children at Oak Creek Elementary receive the new interactive reading program, while the children at Maple Grove Elementary receive standard reading instruction. After six weeks, she compares the vocabulary retention scores between the two schools.
Question: Based on the design of this study, diagnose the group composition. Are the groups in this between-subjects experiment considered equivalent or nonequivalent? Justify your decision based on how the participants were placed into conditions.
Sample answer: The groups in this study are considered nonequivalent. The researcher placed participants into conditions based on the school they already attend rather than using random assignment. Because she relied on these pre-existing groups, the children at the two schools likely possess inherent differences from the outset, making the groups dissimilar.
Key points:
- Diagnoses the groups as nonequivalent.
- Identifies that random assignment was not used.
- Points out that participants were placed based on pre-existing groupings (their schools).
- Explains that the groups likely have pre-existing differences from the outset.
Rubric: Award full credit if the student diagnoses the groups as nonequivalent and justifies this by explaining that random assignment was not used, leading to inherent, pre-existing differences between the schools.
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Research Methods in Psychology - 4th American Edition @ KPU
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