Essay

A research team claims they have conducted an experimental study demonstrating that using daily to-do lists reduces stress, because they compared stress scores of participants using a bar graph. Evaluate this claim by explaining what criteria are necessary to classify a study as experimental rather than correlational, and discuss why the researchers' reliance on the type of graph or variables is insufficient to justify their causal conclusion.

Question: A research team claims they have conducted an experimental study demonstrating that using daily to-do lists reduces stress, because they compared stress scores of participants using a bar graph. Evaluate this claim by explaining what criteria are necessary to classify a study as experimental rather than correlational, and discuss why the researchers' reliance on the type of graph or variables is insufficient to justify their causal conclusion.

Sample answer: To classify a study as experimental, the researcher must manipulate the independent variable by randomly assigning participants to different conditions (e.g., assigning some to make to-do lists and others not to). Comparing variables using a bar graph or studying specific variables does not determine the design. If participants were not randomly assigned but were instead pre-existing groups who were simply asked if they make lists, the design is correlational. A correlational design only allows for the conclusion that the variables are statistically related, not that list-making causes a reduction in stress, due to alternative explanations like the directionality problem (high stress prevents planning) or the third-variable problem (conscientiousness causes both list-making and lower stress).

Key points:

  • A study is defined as experimental or correlational strictly by how it is conducted, not the variables studied or the graphs used.
  • An experiment requires the manipulation of the independent variable through random assignment of participants.
  • A correlational study merely measures variables in pre-existing groups without manipulation.
  • Only experimental designs allow for causal conclusions (e.g., that making to-do lists reduces stress).
  • Correlational studies are subject to the directionality problem (e.g., stress preventing planning) and the third-variable problem (e.g., conscientiousness affecting both).

Rubric: Answers should be evaluated based on: (1) Correct identification of manipulation and random assignment as the defining features of an experiment. (2) Explanation that variables and graphs do not define a study's design. (3) Identification of the limitations of correlational studies, specifically mentioning the inability to draw causal conclusions. (4) Application of the directionality problem and third-variable problem as reasons why a causal conclusion cannot be drawn from correlational 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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