Problem-Solving and Data AnalysisVery hardWhy an experiment beats an observational study here
Problem-Solving and Data Analysis practice question
A study finds that adults who drink green tea daily have lower blood pressure, on average, than adults who do not. A researcher wants to determine whether drinking green tea CAUSES lower blood pressure. Which of the following designs would best let her do so?
- A. Randomly assign volunteers either to drink green tea daily or to drink a similar-tasting placebo, then compare blood pressures after several months.Correct
- B. Survey a much larger group of adults about their tea drinking and blood pressure.
- C. Measure the blood pressure of green-tea drinkers more accurately.
- D. Ask green-tea drinkers whether they believe the tea lowers their blood pressure.
Answer: A. Randomly assign volunteers either to drink green tea daily or to drink a similar-tasting placebo, then compare blood pressures after several months.
Only random assignment breaks the link between tea drinking and other habits (diet, exercise) that could explain the difference.
Why the other answers are wrong
- B. Survey a much larger group of adults about their tea drinking and blood pressure.
- A bigger observational study has the same confounding problem as the small one.
- C. Measure the blood pressure of green-tea drinkers more accurately.
- More precise measurement doesn't address why the groups differ.
- D. Ask green-tea drinkers whether they believe the tea lowers their blood pressure.
- Beliefs are not evidence of cause.
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