Case Study

Analyze this case study. Diagnose the primary scientific error in the researcher's conclusion as reported by the media. Then, decide what type of research design is required to truly determine if childhood candy consumption causes adult violent behavior, and justify your choice based on the limitations of the current study's observational data.

Case context: A developmental psychologist reads a news article summarizing a longitudinal study. The article headline reads, 'Sweets Today, Handcuffs Tomorrow: Childhood Candy Habits Predict Adult Aggression.' The study followed 500 children over 20 years and found a significant statistical association between the frequency of childhood candy intake and the number of arrests for violent crimes in adulthood. The researcher who conducted the study is quoted saying, 'Our findings show that to reduce violent crime, parents need to restrict their children's sugar intake.'

Question: Analyze this case study. Diagnose the primary scientific error in the researcher's conclusion as reported by the media. Then, decide what type of research design is required to truly determine if childhood candy consumption causes adult violent behavior, and justify your choice based on the limitations of the current study's observational data.

Sample answer: The primary scientific error is implying causation from correlational (observational) data. The researcher claims that restricting sugar intake will reduce violent crime, which assumes a causal link where candy consumption directly leads to violence, ignoring potential third variables. To prove causation, a controlled experiment is required. In a controlled experiment, the researcher would randomly assign children to different levels of daily candy consumption while controlling other environmental variables, and then measure subsequent aggressive behavior. This design is justified because random assignment minimizes the influence of confounding third variables, allowing the researcher to isolate the causal effect of diet on behavior, which observational data cannot do.

Key points:

  • Diagnoses the error of assuming a causal link from a statistical association/observational data.
  • Notes that the conclusion ignores potential third variables.
  • Decides that a controlled experiment is the necessary research design to establish causation.
  • Justifies the controlled experiment by explaining that it controls variables or uses random assignment to isolate the causal effect.

Rubric: The response must diagnose the correlation-causation error (implying causation from observational data and ignoring third variables). It must decide that a controlled experiment is required to establish causation. It must justify this choice by explaining how controlled experiments (e.g., via random assignment or manipulation) address the limitations of observational data.

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Updated 2026-05-27

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Research Methods in Psychology - 4th American Edition @ KPU

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