Evaluating Statistical Claims: Observational Studies and Experiments Flashcards
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A researcher observes that cities with more coffee shops have higher average incomes. The researcher concludes that opening more coffee shops causes income to rise. What is the primary flaw in this reasoning?
Answer: Correlation does not imply causation; a confounding variable may explain both.
Observational studies can identify associations but cannot establish causation because confounding variables (e.g., city wealth) may explain both variables.
A study randomly assigns 200 volunteers to two groups: Group A takes a vitamin supplement daily and Group B takes a placebo for 6 months. At the end, Group A reports significantly fewer colds. What conclusion is best supported?
Answer: The supplement may cause a reduction in colds among people similar to those in this study.
Randomized experiments support causal conclusions, but the results can only be generalized to populations similar to those in the study.
A school district surveys 500 randomly selected students across all its schools about their reading habits and finds that students who read more also have higher GPA. Can the district conclude that reading more causes higher GPA?
Answer: No, because this is an observational study and causation cannot be inferred from correlation.
Even with random sampling, observational studies cannot establish causation because subjects were not randomly assigned to treatments; a third variable could explain the relationship.
Researchers conduct a study in which participants are randomly assigned to eat breakfast or skip it, then measure their morning productivity for 4 weeks. The breakfast group showed significantly higher productivity. Which conclusion is best supported?
Answer: For people similar to study participants, eating breakfast likely causes higher morning productivity.
Random assignment supports a causal conclusion, but generalizability is limited to populations similar to those studied.
A nutritionist conducts an observational study of 1,000 adults and finds that those who eat fish twice a week have lower rates of heart disease. Which of the following is the most appropriate conclusion?
Answer: There is an association between eating fish and lower rates of heart disease in this sample.
An observational study can only identify associations, not causal relationships, since participants were not randomly assigned to a diet.
A medical study randomly selects 300 patients from a clinic in one city, then randomly assigns half to a new treatment and half to standard care. The new treatment shows better outcomes. To which population can the results be most validly generalized?
Answer: Patients similar to those at this clinic who would be eligible for the treatment
Because the sample was drawn from one clinic, results can be generalized to similar patients at that type of clinic, not to all patients globally.
A study finds that people who own pets have lower blood pressure. A journalist writes: 'Owning a pet reduces blood pressure.' Which error did the journalist make?
Answer: Concluding causation from an observational association
The journalist incorrectly inferred a causal relationship from an observational association; confounding variables (e.g., lifestyle, stress level) may explain the link.