Evaluating Statistical Claims: Observational Studies and Experiments Flashcards

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?

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

Random assignment supports a causal conclusion; however, generalizability is limited to populations similar to the study participants.

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?

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

Counties with more libraries likely invest more in education overall, making community investment a confounding variable that could explain both library visits and graduation rates.

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?

Answer: People in cities similar to the 10 cities studied

Random selection from 10 cities supports generalization to populations in similar cities; random assignment supports causal inference but does not expand the scope of generalizability.

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?

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

Confounding lifestyle factors (e.g., exercise, smoking, stress management) common among vegetarians could explain the lower diabetes rate, undermining a causal claim.

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?

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

Volunteers may be more motivated or open to technology than the general adult population, limiting how well the results generalize beyond similar volunteers.

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?

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

The key question is whether the study used random assignment; without it, healthier people may already be more likely to take vitamins, making causation impossible to conclude.

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?

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

Neighborhood wealth is a confounding variable that could explain both higher security system ownership and lower crime rates, making the causal claim unsupported.