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Case Study

Explain why this specific two-condition experimental design resulted in lower construct validity. What alternative psychological phenomenon might this design demonstrate instead of diffusion of responsibility, and how would expanding the design address this issue?

Case context: A researcher is conducting a study on bystander intervention. Drawing from Darley and Latané's work, the researcher sets up an experiment with only two conditions: one where the participant is alone (one-person condition) and one where the participant is with one other student (two-person condition). The researcher finds that helping behavior decreases in the two-person condition and concludes this is a clear demonstration of the diffusion of responsibility.

Question: Explain why this specific two-condition experimental design resulted in lower construct validity. What alternative psychological phenomenon might this design demonstrate instead of diffusion of responsibility, and how would expanding the design address this issue?

Sample answer: Testing only two conditions (one versus two other students) results in lower construct validity because it fails to isolate the specific mechanism of diffusion of responsibility. Instead of demonstrating diffusion of responsibility, the decrease in helping might merely demonstrate general social inhibition due to the presence of others. Expanding the experiment to include multiple conditions helps clarify the phenomenon by showing how helping behavior changes as the group size increases, though adding too many conditions may eventually plateau without adding further insight.

Key points:

  • Testing only two conditions might merely demonstrate general social inhibition rather than specific diffusion of responsibility, leading to lower construct validity.
  • The presence of one other student fails to isolate the specific psychological phenomenon of interest.
  • Expanding the study to multiple conditions clarifies the phenomenon.
  • Adding too many conditions may eventually plateau without adding further insight.

Rubric: The student must explain that testing only two conditions results in lower construct validity because it fails to isolate diffusion of responsibility from general social inhibition. They must identify general social inhibition (or the mere presence of others) as the alternative explanation, and explain that expanding to multiple conditions helps clarify the phenomenon, while noting that adding too many conditions may plateau without adding further insight.

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Updated 2026-05-26

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Research Methods in Psychology - 4th American Edition @ KPU

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