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Based on the provided scenario, diagnose the type of research design used and explain why the threat of potential confounding variables is significantly elevated in this study compared to a true experiment.
Case context: A developmental psychology researcher wants to study the effect of a new interactive reading program on vocabulary acquisition. The researcher conducts the study at a local elementary school. Classroom A receives the new interactive reading program, while Classroom B continues with the standard reading curriculum. At the end of the term, the researcher compares the vocabulary scores of the two classrooms.
Question: Based on the provided scenario, diagnose the type of research design used and explain why the threat of potential confounding variables is significantly elevated in this study compared to a true experiment.
Sample answer: This is a nonequivalent groups design because intact classrooms were used and participants were not randomly assigned to the reading programs. Without random assignment, the two classes likely have inherent, pre-existing differences (such as different baseline abilities or teacher experience). These initial dissimilarities introduce potential confounding variables that significantly threaten the internal validity of the research, as any difference in final scores might be caused by these pre-existing differences rather than the reading program.
Key points:
- The scenario describes a nonequivalent groups design (a quasi-experimental approach).
- The researcher did not use random assignment to allocate students to Classroom A or Classroom B.
- The lack of random assignment means the groups are likely nonequivalent with inherent, pre-existing differences.
- These initial dissimilarities introduce potential confounding variables that threaten the study's internal validity.
Rubric: Full credit is awarded if the student correctly identifies the nonequivalent groups design, notes the absence of random assignment, and explains that pre-existing differences create confounding variables that threaten internal validity.
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Research Methods in Psychology - 4th American Edition @ KPU
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