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Analyze Dr. Alvarez's experimental design. Identify the critical design flaw that allowed the fatigue effect to occur, and explain how this carryover effect acts as a confounding variable that invalidates the researcher's conclusion about the noise levels.
Case context: Dr. Alvarez conducts a within-subjects experiment to test how three different background noise levels (Silent, Classical Music, and Loud Construction Noise) affect participant problem-solving speeds. All participants perform the Silent condition first for 30 minutes, followed immediately by the Classical Music condition for 30 minutes, and finally the Loud Construction Noise condition for 30 minutes. Dr. Alvarez finds that problem-solving speed is significantly slower in the final Loud Construction Noise condition. However, a peer reviewer argues that these findings are invalid due to a fatigue effect.
Question: Analyze Dr. Alvarez's experimental design. Identify the critical design flaw that allowed the fatigue effect to occur, and explain how this carryover effect acts as a confounding variable that invalidates the researcher's conclusion about the noise levels.
Sample answer: The critical flaw in Dr. Alvarez's design is the lack of control over the order of conditions, as all participants completed the conditions in the exact same sequence. Because the Loud Construction Noise condition was always last, participants had already spent 60 minutes solving problems and likely became physically tired, mentally exhausted, or bored. Slower problem-solving speed in this final condition could simply be a fatigue effect rather than a result of the loud construction noise. This fatigue effect acts as a confounding variable because it introduces an alternative explanation for the decline in performance, thereby obscuring the true effect of the independent variable (noise level).
Key points:
- The order of conditions was not properly controlled by the researcher.
- Participants perform worse in later conditions due to physical/mental tiredness or boredom from earlier conditions.
- The performance decline serves as a confounding variable in this design.
- The confounding variable obscures the true effect of the independent variable (noise levels).
Rubric: Answers should identify: 1) The lack of control over the order of conditions as the main design flaw; 2) Slower performance in the construction noise condition could be due to tiredness or boredom from the prior 60 minutes of testing; 3) The fatigue effect is a specific carryover effect that acts as a confounding variable; and 4) It creates an alternative explanation that invalidates the conclusion about the noise levels.
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Research Methods in Psychology - 4th American Edition @ KPU
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