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Case Study

Based on the concept of extraneous variables, diagnose what type of variables writing ability and diet represent in this specific experiment, and explain what these variables might do to the dependent variable if left unaddressed.

Case context: A researcher is conducting an experiment to test the effect of expressive writing on health. Before the experiment begins, the researcher notes that the individuals involved have varying levels of baseline writing ability and follow vastly different diets.

Question: Based on the concept of extraneous variables, diagnose what type of variables writing ability and diet represent in this specific experiment, and explain what these variables might do to the dependent variable if left unaddressed.

Sample answer: Writing ability and diet represent participant variables, also known as individual differences. If left unaddressed, these pre-existing characteristics are likely to have their own independent effect on the dependent variable (health), thereby obscuring the true effect of the experimental manipulation (the expressive writing).

Key points:

  • Writing ability and diet are classified as participant variables or individual differences.
  • These variables represent pre-existing characteristics of the individuals involved.
  • They are likely to exert an independent effect on the dependent variable.
  • If not controlled, they may obscure the actual effect of the experimental manipulation.

Rubric: The student correctly identifies the factors as participant variables (or individual differences) and demonstrates comprehension by explaining their potential to independently affect the dependent variable and obscure the experimental effect.

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Updated 2026-05-27

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Research Methods in Psychology - 4th American Edition @ KPU

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