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Based on the characteristics of an AB design, explain why the psychologist cannot confidently conclude that the checklist caused the increase in on-task behavior, identifying the specific threat to internal validity present in this scenario.
Case context: A school psychologist is investigating whether a self-monitoring checklist increases a student's on-task behavior during quiet study time. For one week, the psychologist measures baseline on-task behavior (Phase A). At the start of the second week, the checklist is introduced (Phase B), and the student's on-task behavior immediately increases. However, the psychologist learns that the student's teacher also reorganized the classroom seating arrangement at the beginning of the second week.
Question: Based on the characteristics of an AB design, explain why the psychologist cannot confidently conclude that the checklist caused the increase in on-task behavior, identifying the specific threat to internal validity present in this scenario.
Sample answer: The psychologist cannot confidently attribute the change in behavior to the checklist because the classroom seating rearrangement acts as a confounding extraneous variable. Because the AB design only involves two phases (baseline to treatment) without a reversal phase, any coincidental change occurring at the start of Phase B introduces ambiguity. It remains unclear whether the checklist or the new seating arrangement caused the increase in on-task behavior, demonstrating the low internal validity of the AB design.
Key points:
- The seating rearrangement is an extraneous variable that coincided with Phase B.
- An AB design cannot differentiate between the effects of the treatment and coincidental external events.
- The lack of a reversal phase prevents ruling out the confounding variable.
- The internal validity of the causal claim is compromised.
Rubric: Grading criteria: 1) Student must identify the seating rearrangement as a coincidental extraneous or confounding variable. 2) Student must explain that because the seating change occurred at the same time as the intervention phase (B), its effects cannot be separated from the treatment. 3) Student must connect this limitation to the overall low internal validity of the AB design.
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Research Methods in Psychology - 4th American Edition @ KPU
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