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Based on the assumptions of single-subject research, diagnose the methodological flaw in the researcher's conclusion. Explain how this flaw violates the core assumptions needed to establish a causal relationship and describe its impact on the study's internal validity.
Case context: A clinical researcher wants to determine if a new biofeedback device reduces a patient's physiological anxiety. The researcher measures the patient's heart rate (dependent variable) daily. In the second week, the researcher introduces the biofeedback device (independent variable). However, during this second week, the patient also starts a new daily exercise routine and begins drinking double their usual amount of caffeine. The researcher notices a decrease in the patient's heart rate and concludes that the biofeedback device caused this change.
Question: Based on the assumptions of single-subject research, diagnose the methodological flaw in the researcher's conclusion. Explain how this flaw violates the core assumptions needed to establish a causal relationship and describe its impact on the study's internal validity.
Sample answer: The researcher's conclusion is flawed because they did not carefully control extraneous variables (the patient's new exercise routine and increased caffeine intake). The core assumption of single-subject research is that causal relationships can only be effectively discovered if extraneous variables are controlled while manipulating the independent variable and measuring the dependent variable. Because these extraneous variables were not controlled, they act as confounding variables, making it impossible to determine if the biofeedback device, the exercise, or the caffeine caused the change in heart rate. Consequently, the study's internal validity is severely weakened.
Key points:
- The researcher failed to carefully control extraneous variables (exercise and caffeine).
- Controlling extraneous variables is a key assumption for discovering causal relationships in single-subject research.
- Uncontrolled extraneous variables act as confounds, preventing a clear causal conclusion.
- The lack of control compromises the study's internal validity.
Rubric: To receive full credit, the answer must: 1. Identify the lack of control over extraneous variables (exercise and caffeine) as the primary methodological flaw (2 points). 2. Explain that controlling extraneous variables is a core assumption required to establish causal relationships in single-subject research (2 points). 3. State that this failure introduces confounding variables and weakens the study's internal validity (1 point).
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Research Methods in Psychology - 4th American Edition @ KPU
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