Bluebook SAT Test Evaluating Statistical Claims: Observational Studies and Experiments 7 — Questions and Answers
Question 1: A news headline reads: 'Students who eat lunch perform better in afternoon classes.' The data came from a study where students chose whether to eat lunch. Which of the following is most likely a confounding variable?
- The type of food served in the cafeteria
- Overall health and family habits that affect both eating patterns and academic performance (Correct answer)
- The time of day the afternoon classes are scheduled
- The grade level of the students
Correct answer: Overall health and family habits that affect both eating patterns and academic performance
Students from families that emphasize regular meals may also emphasize studying and routines, making family habits a confounding variable associated with both lunch-eating and academic performance.
Question 2: A pharmaceutical company randomly assigns 1,000 patients with high blood pressure to either a new medication or a placebo. After 6 months, the medication group shows a significant reduction in blood pressure. The company claims the medication is effective for all patients with high blood pressure. What is the most valid concern?
- Placebos are never appropriate in blood pressure studies.
- The study sample may not represent all patients with high blood pressure, such as those with other conditions. (Correct answer)
- Blood pressure cannot be measured accurately in randomized trials.
- The 6-month period is too long for a blood pressure study.
Correct answer: The study sample may not represent all patients with high blood pressure, such as those with other conditions.
Random assignment supports causation within the sample, but the sample's characteristics (e.g., age, comorbidities) may limit how broadly the results apply.
Question 3: Researchers observe that countries with more hospitals per capita also have longer life expectancy. They conclude that building more hospitals increases life expectancy. What is the most likely confounding variable?
- The number of doctors per hospital
- National wealth, which increases both hospital capacity and access to food, education, and clean water (Correct answer)
- Geographic size of the country
- The age distribution of each country's population
Correct answer: National wealth, which increases both hospital capacity and access to food, education, and clean water
Wealthier nations can afford more hospitals and also have better nutrition, education, sanitation, and healthcare access — all of which increase life expectancy independently.
Question 4: A social scientist conducts an experiment by randomly assigning rural communities to receive a new community center and comparing crime rates to communities that did not receive one. After 2 years, crime rates are lower in communities with the center. What is the scope of the valid causal conclusion?
- Community centers cause lower crime rates in all cities globally.
- In rural communities similar to those studied, community centers likely cause lower crime rates. (Correct answer)
- Crime rates would have dropped even without the community centers.
- There is only a correlation, not a causal relationship, between centers and crime.
Correct answer: In rural communities similar to those studied, community centers likely cause lower crime rates.
Random assignment supports causation; the causal conclusion applies to rural communities similar to those in the study, not to all communities globally.
Question 5: A study surveys 800 teenagers about sleep habits and academic performance. Students who sleep 9 or more hours have higher GPA. A parent concludes that forcing teens to sleep 9 hours will improve their grades. Why is this conclusion flawed?
- GPA is not a good measure of academic performance.
- The association is from an observational study; factors like family structure and health may cause both more sleep and higher GPA. (Correct answer)
- Teenagers cannot control their sleep schedules.
- The survey sample of 800 is too small to draw conclusions.
Correct answer: The association is from an observational study; factors like family structure and health may cause both more sleep and higher GPA.
Observational studies cannot establish that sleep causes higher GPA; structured home environments may promote both longer sleep and better academic habits.
Question 6: Two researchers study the effect of tutoring on test scores. Researcher A randomly assigns students to tutoring or no tutoring. Researcher B surveys students who chose to get tutoring vs. those who didn't. Which researcher can draw causal conclusions, and why?
- Researcher B, because voluntary participation increases motivation.
- Researcher A, because random assignment controls for confounding variables. (Correct answer)
- Both researchers, because both measure tutoring and test scores.
- Neither researcher, because test scores have too many influences.
Correct answer: Researcher A, because random assignment controls for confounding variables.
Only Researcher A used random assignment, which balances confounders between groups and allows a causal conclusion; Researcher B's study is observational and subject to selection bias.
Question 7: A report states: 'Among 500 randomly selected adults, those who meditate have lower cortisol levels.' A journalist writes: 'Meditation reduces cortisol.' What is wrong with the journalist's conclusion?
- Cortisol levels cannot be measured in a sample of 500.
- The study used a random sample but did not randomly assign participants to meditate, so causation cannot be concluded. (Correct answer)
- The journalist should have reported the confidence interval for cortisol levels.
- A random sample is not appropriate for studying meditation habits.
Correct answer: The study used a random sample but did not randomly assign participants to meditate, so causation cannot be concluded.
The study is observational — people who chose to meditate may differ in other ways (stress management, lifestyle) from those who don't, making the causal claim unjustified.
Bluebook SAT Test Evaluating Statistical Claims: Observational Studies and Experiments 7
A news headline reads: 'Students who eat lunch perform better in afternoon classes.' The data came from a study where students chose whether to eat lunch.
Which of the following is most likely a confounding variable?