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Explain how observer fatigue in this scenario represents an instrumentation threat to internal validity, and explain why the psychologist cannot conclude that the sharing intervention was successful based on these results.
Case context: A developmental psychologist evaluates the effectiveness of a classroom sharing intervention using a one-group pretest-posttest design. During the pretest observations, the observers are highly alert and strictly code child interactions. By the posttest, the observers are tired and unconsciously relax their standards, resulting in fewer interactions being coded as uncooperative.
Question: Explain how observer fatigue in this scenario represents an instrumentation threat to internal validity, and explain why the psychologist cannot conclude that the sharing intervention was successful based on these results.
Sample answer: This scenario represents an instrumentation threat because the instrument of measurement (the human observers) changed its evaluation standards between the pretest and the posttest due to fatigue. Because the coding standards became more lenient, the recorded decrease in uncooperative behavior could simply be a result of this measurement change rather than a real improvement in the children's behavior. Therefore, internal validity is compromised, and the psychologist cannot determine whether the sharing intervention or the altered observation standards caused the change.
Key points:
- Identify that the human observers function as the measuring instrument.
- Explain that observer fatigue led to a change in evaluation standards between pretest and posttest.
- Conclude that this change prevents the researcher from attributing the behavioral difference to the intervention.
Rubric: The response must identify that the change in recorded behavior is due to changes in observer standards (fatigue) rather than child behavior, and explain that this confound makes it impossible to isolate the intervention's effect, thereby threatening internal validity.
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Research Methods in Psychology - 4th American Edition @ KPU
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