Bluebook SAT Test Evaluating Statistical Claims: Observational Studies and Experiments 3 — Questions and Answers
Question 1: A researcher randomly selects 1,000 adults from across the United States and finds that adults who sleep 8 hours per night report higher life satisfaction. Which statement is best supported by this study?
- Sleeping 8 hours per night causes higher life satisfaction in U.S. adults.
- There is an association between sleeping 8 hours and higher life satisfaction that is likely representative of U.S. adults. (Correct answer)
- All U.S. adults should sleep exactly 8 hours per night.
- The study proves that sleep quality is more important than sleep quantity.
Correct answer: There is an association between sleeping 8 hours and higher life satisfaction that is likely representative of U.S. adults.
The random sample supports generalization to U.S. adults, but because this is observational (no random assignment), only an association — not causation — can be concluded.
Question 2: A study randomly assigns participants to two diet groups for 12 weeks: a high-protein diet or a standard diet. The high-protein group loses significantly more weight. Which conclusion is best supported?
- A high-protein diet causes more weight loss among people similar to study participants. (Correct answer)
- All people who try a high-protein diet will lose more weight.
- There is only a correlation between diet and weight loss, not a causal link.
- The standard diet group's results are invalid because they served as a control.
Correct answer: A high-protein diet causes more weight loss among people similar to study participants.
Random assignment allows a causal conclusion; however, the result only generalizes to populations similar to the study participants.
Question 3: An observational study follows 5,000 people over 20 years and finds that those who regularly volunteer have longer lifespans. What is the most important limitation of this finding?
- The study followed too few people to be meaningful.
- Since participants were not randomly assigned to volunteer or not, the association could be due to confounding variables such as overall health or social status. (Correct answer)
- Volunteering cannot be measured objectively.
- The 20-year period is too short to assess lifespan effects.
Correct answer: Since participants were not randomly assigned to volunteer or not, the association could be due to confounding variables such as overall health or social status.
Without random assignment, people who volunteer may differ systematically (e.g., better health, higher income) from those who don't, making it impossible to attribute longer life to volunteering.
Question 4: A school randomly selects 80 students to participate in a new after-school reading program and observes that they read better at year-end than a comparison group. Which aspect of the study design limits the strength of a causal conclusion?
- The sample of 80 students is too small for any conclusion.
- The students were randomly selected but not randomly assigned to treatment and control groups. (Correct answer)
- Reading improvement cannot be measured accurately in schools.
- The study should have been conducted over multiple years.
Correct answer: The students were randomly selected but not randomly assigned to treatment and control groups.
Random selection determines who is in the study (generalizability), but random assignment is needed to form comparable treatment and control groups; without it, the causal link is uncertain.
Question 5: A poll randomly samples 2,000 U.S. adults and finds that 65% support stricter environmental regulations. Based on this, which conclusion is valid?
- Stricter environmental regulations will pass in the next election.
- Approximately 65% of U.S. adults support stricter environmental regulations. (Correct answer)
- Every U.S. adult either supports or opposes stricter regulations with equal probability.
- The result proves that environmental concerns cause political preferences.
Correct answer: Approximately 65% of U.S. adults support stricter environmental regulations.
A large random sample of U.S. adults supports a generalization about the population; however, this is descriptive — no causal claims about causes of political preferences can be drawn.
Question 6: A study randomly assigns 300 volunteers to meditate for 20 minutes daily or to sit quietly for 20 minutes daily and then measures their stress levels. Which of the following questions can the study best answer?
- Does meditation lower stress compared to quiet sitting for people like those in the study? (Correct answer)
- Does meditation lower stress for all people worldwide?
- Is there a correlation between meditation habits and personality type?
- Would stress levels have changed even without the intervention?
Correct answer: Does meditation lower stress compared to quiet sitting for people like those in the study?
The randomized experiment with a control group can address whether meditation causes lower stress relative to quiet sitting, but only for populations similar to the volunteers.
Question 7: In a study of exercise and mood, participants self-selected into either an exercise group or a sedentary group. Those who exercised reported better moods. Which design change would most improve the ability to conclude that exercise causes better mood?
- Increasing the sample size
- Randomly assigning participants to the exercise or sedentary group (Correct answer)
- Surveying participants about their mood before the study
- Conducting the study over a longer time period
Correct answer: Randomly assigning participants to the exercise or sedentary group
Random assignment would eliminate selection bias (e.g., motivated people choosing exercise) and allow a causal conclusion to be drawn.
Bluebook SAT Test Evaluating Statistical Claims: Observational Studies and Experiments 3
A researcher randomly selects 1,000 adults from across the United States and finds that adults who sleep 8 hours per night report higher life satisfaction.
Which statement is best supported by this study?