Case Study

Based on the details of this study, explain how the researchers' choice of a correlational design rather than an experimental lab design affects both the internal and external validity of their findings. Why does measuring these variables in their natural state lead to these specific validity outcomes?

Case context: A research team is investigating the relationship between daily caffeine consumption and nighttime sleep duration. Instead of bringing participants into a sleep laboratory where caffeine intake and bedtime are strictly controlled, the researchers decide to track participants' self-reported daily coffee intake and actual sleep times in their normal home environments.

Question: Based on the details of this study, explain how the researchers' choice of a correlational design rather than an experimental lab design affects both the internal and external validity of their findings. Why does measuring these variables in their natural state lead to these specific validity outcomes?

Sample answer: By choosing a correlational design to measure caffeine intake and sleep duration in their natural state, the researchers cannot manipulate or control any variables, which results in low internal validity. However, because the study observes these variables exactly as they naturally occur in the participants' real lives rather than in an artificial laboratory, the findings are more likely to reflect real-world phenomena, granting the study high external validity.

Key points:

  • The researchers do not manipulate caffeine intake or sleep conditions, resulting in low internal validity.
  • Variables are measured exactly as they naturally occur in the participants' everyday environment.
  • Natural measurement avoids the artificial conditions of a sleep laboratory.
  • The lack of experimental control allows the results to better reflect real-world relationships, giving the study high external validity.

Rubric: The response must demonstrate comprehension of validity trade-offs within the case study context. Specifically, the student must explain that natural measurement without manipulation leads to low internal validity (lack of control) but high external validity (results represent real-world phenomena).

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Updated 2026-05-27

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Research Methods in Psychology - 4th American Edition @ KPU

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