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Case Study

Based on the concept of internal validity described in the text, identify whether this study has high or low internal validity. Explain why this non-experimental correlational design cannot justify the researcher's causal conclusion, and describe at least one alternative explanation (such as reverse causation or extraneous factors) for the observed link.

Case context: A psychologist conducts a study where they survey 200 participants and find a strong statistical relationship between the number of hours they spend exercising each week and their self-reported happiness scores. The researcher publishes a report concluding that regular exercise is the direct cause of increased happiness.

Question: Based on the concept of internal validity described in the text, identify whether this study has high or low internal validity. Explain why this non-experimental correlational design cannot justify the researcher's causal conclusion, and describe at least one alternative explanation (such as reverse causation or extraneous factors) for the observed link.

Sample answer: This study has low internal validity. Since it uses a non-experimental correlational design, the variables are measured but not manipulated, which means the design cannot justify the conclusion that exercise directly caused changes in happiness. Alternative explanations, such as reverse causation (happier people choosing to exercise more) or extraneous variables (like overall health or income), could explain the correlation instead.

Key points:

  • The study exhibits low internal validity because it uses a non-experimental correlational design.
  • Non-experimental designs measure variables without experimenter manipulation, which cannot justify causal conclusions.
  • Alternative explanations, including reverse causation or extraneous factors, might explain the statistical relationship.

Rubric: The response must correctly identify the study as having low internal validity and specify that this is due to its non-experimental correlational design. It must explain that because variables are not manipulated, a direct causal relationship cannot be confirmed. Finally, it must offer at least one valid alternative explanation, such as reverse causation or other extraneous factors.

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Updated 2026-05-27

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Research Methods in Psychology - 4th American Edition @ KPU

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