Diagnose why the lack of a manipulation check prevents the researchers from understanding this null result. Specifically, explain what two distinct explanations for the result they are unable to differentiate.
Case context: A research group performs an experiment testing a new teaching method (independent variable) on student test scores (dependent variable). They find no significant difference in test scores between the experimental group and the control group, resulting in a null result. The researchers did not include a manipulation check to verify if the experimental group actually experienced the new teaching method differently from the control group.
Question: Diagnose why the lack of a manipulation check prevents the researchers from understanding this null result. Specifically, explain what two distinct explanations for the result they are unable to differentiate.
Sample answer: Without a manipulation check, the researchers cannot determine if the new teaching method was actually implemented successfully. Thus, they cannot tell if the null result occurred because the teaching method genuinely has no effect on test scores, or because the experimental manipulation failed to actually alter the independent variable (the teaching experience) as intended.
Key points:
- The lack of a manipulation check makes it impossible to know if the independent variable was altered.
- Explanation one: The independent variable genuinely has no effect on the dependent variable (student test scores).
- Explanation two: The experimental manipulation itself failed to alter the independent variable (teaching method exposure) as intended.
- Without the check, these two explanations cannot be distinguished.
Rubric: The response must explain that a manipulation check is needed to confirm the success of the manipulation. It should state that without it, the researchers cannot distinguish whether the teaching method genuinely has no effect on test scores, or if the manipulation itself failed to alter the independent variable.
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Research Methods in Psychology - 4th American Edition @ KPU
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