Bluebook SAT Test Evaluating Statistical Claims: Observational Studies and Experiments 5

Question 1

A study randomly assigns 200 participants to either a sleep restriction group (6 hours/night) or a normal sleep group (8 hours/night) for 2 weeks.
The restricted sleep group performs worse on memory tests.
What is the most valid conclusion?

Accepted Answer

For people similar to those in this study, sleep restriction likely causes worse memory performance.

Answer

Sleep restriction causes memory impairment in all adults.

Answer

Memory tests are unreliable for measuring sleep effects.

Answer

There is only a correlation between sleep and memory, not a causal relationship.

Question 2

A researcher observes that counties with higher rates of library visits also have higher graduation rates. She claims that library use causes higher graduation rates. What is wrong with her reasoning?

Accepted Answer

The association might be explained by a confounding variable, such as overall community investment in education.

Answer

Graduation rates are not a valid outcome to measure.

Answer

She needs a larger county-level sample to make any claim.

Answer

Observational studies cannot show any kind of relationship.

Question 3

Participants in a study are randomly selected from 10 different cities and randomly assigned to either an intervention or control group. The intervention group shows a significant positive outcome. To which population can results be most validly generalized?

Accepted Answer

People in cities similar to the 10 cities studied

Answer

All people in the world

Answer

Only the people who were in the intervention group

Answer

All adults in the country where the cities are located

Question 4

A study of 10,000 adults finds that vegetarians have lower rates of type 2 diabetes than non-vegetarians. A nutritionist claims this proves vegetarian diets prevent diabetes. What is the most valid critique?

Accepted Answer

Vegetarians may differ from non-vegetarians in other healthy behaviors (exercise, lower smoking) that reduce diabetes risk, making causation unclear.

Answer

The study is too large; smaller studies are more valid.

Answer

Diabetes rates cannot be observed in non-experimental studies.

Answer

The nutritionist's claim is valid because the sample size is large enough to prove causation.

Question 5

A randomized experiment gives one group a mindfulness app and the other no app, then measures anxiety. The app group reports lower anxiety. Which of the following would most limit generalizing this result to all adults?

Accepted Answer

Participants volunteered for the study, so they may not represent all adults.

Answer

The random assignment process introduced bias.

Answer

The experiment lasted too long.

Answer

The anxiety measure was self-reported.

Question 6

An article reports: 'A study found people who take daily vitamins are healthier than those who don't.' The article concludes vitamins cause better health. Which question would most directly test whether this conclusion is valid?

Accepted Answer

Was this an observational study or a randomized experiment with random assignment?

Answer

How many vitamins were taken per day?

Answer

Were the vitamins taken in the morning or evening?

Answer

What brand of vitamins was used in the study?

Question 7

A city randomly selects 500 households and surveys them about neighborhood crime and home security systems. They find a negative correlation: more security systems, fewer reported crimes. A council member says security systems reduce crime. What is the main limitation?

Accepted Answer

Wealthier neighborhoods may have more security systems and also have fewer crimes for unrelated reasons, making the causal claim unjustified.

Answer

The sample of 500 households is too small for city-wide conclusions.

Answer

Correlation can never be found in survey data.

Answer

City councils cannot use survey data for policy decisions.