Case Study

Based on your understanding of researcher characteristics as extraneous variables, explain how the experimenter's biological sex functioned in this study. Describe the underlying mechanism of this phenomenon and explain why it confounds the study's ability to draw clear conclusions about the stress manipulation.

Case context: A research group is investigating the effects of stress on heart rate. Half of the participants are tested by a male experimenter, and the other half are tested by a female experimenter. The researchers note that participants assigned to the opposite-sex experimenter report lower subjective stress and show lower heart rates than those tested by the same-sex experimenter, regardless of the actual stress manipulation. The researchers are confused as to why their stress manipulation did not show the expected main effect.

Question: Based on your understanding of researcher characteristics as extraneous variables, explain how the experimenter's biological sex functioned in this study. Describe the underlying mechanism of this phenomenon and explain why it confounds the study's ability to draw clear conclusions about the stress manipulation.

Sample answer: In this study, the experimenter's biological sex functioned as an extraneous variable that confounded the results. The underlying mechanism is that male and female experimenters interact differently with subjects, and subjects respond differently depending on whether the experimenter is of the same or opposite sex (such as showing altered stress levels or physiological responses in opposite-sex pairings). This confounds the study because the variation in heart rate and subjective stress is caused by the experimenter-participant sex dynamic rather than the independent variable (the stress manipulation), making it impossible to isolate the true effect of stress.

Key points:

  • Identify the experimenter's sex as an extraneous variable.
  • Explain that participants respond differently to opposite-sex versus same-sex experimenters (affecting stress/heart rate).
  • Describe how this variation confounds the independent variable (stress manipulation).
  • Understand that male and female researchers interact differently with subjects.

Rubric: The answer should explain that the experimenter's sex is an extraneous variable because participants reacted differently to opposite-sex versus same-sex experimenters. It should comprehend that this difference in interactions and responses introduces systematic variation (noise/confound) that obscures the true effect of the independent variable (stress manipulation).

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Updated 2026-05-27

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Research Methods in Psychology - 4th American Edition @ KPU

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