Case Study

Based on the principles of reversal designs, explain why Dr. Aris cannot confidently conclude that the token economy system caused the reduction in disruptive behavior. Diagnose the threat to internal validity and justify your decision based on the behavior's failure to revert.

Case context: Dr. Aris is investigating whether a new classroom token economy system reduces disruptive behavior in a student. Dr. Aris establishes a baseline of disruptive behavior (A), implements the token economy system (B), and observes a substantial decrease in disruptive behavior. Dr. Aris then withdraws the token economy system (A) to complete a reversal design. However, even after the system is removed, the student's disruptive behavior remains low and does not return to baseline levels.

Question: Based on the principles of reversal designs, explain why Dr. Aris cannot confidently conclude that the token economy system caused the reduction in disruptive behavior. Diagnose the threat to internal validity and justify your decision based on the behavior's failure to revert.

Sample answer: Dr. Aris cannot confidently conclude causality because the behavior did not revert to baseline levels when the token economy was removed. In a reversal design, internal validity depends on showing that behavior changes in response to both the introduction and the removal of the treatment. Because the disruptive behavior remained low, it is unclear whether the token economy caused the initial change, or if an extraneous variable (such as learning a new long-term habit, maturation, or a change in classroom dynamics) was responsible. Since the treatment's effects may be permanent or co-occurring with an extraneous variable, the reversal design failed to rule out alternative explanations, compromising internal validity.

Key points:

  • Causality cannot be demonstrated because the dependent variable failed to revert to baseline upon treatment removal.
  • Internal validity in a reversal design relies on behavior reverting to rule out extraneous variables.
  • A lack of reversion indicates the treatment's effects might be permanent or that an extraneous variable caused the change.
  • Without the reversion phase working as intended, the study cannot rule out alternative explanations for the change.

Rubric: A complete response should: 1) Explain that the lack of reversion to baseline prevents establishing causality; 2) Identify that without reversion, extraneous variables cannot be ruled out; 3) Note that the lack of reversion might indicate the treatment's effects are permanent or that another factor caused the change; and 4) Explain that this failure to revert compromises the internal validity of the study.

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Updated 2026-05-27

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Research Methods in Psychology - 4th American Edition @ KPU

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