Evaluating Statistical Claims: Observational Studies and Experiments Flashcards

A study randomly assigns 200 adults to either a daily walking program or a sedentary control group for 8 weeks. The walking group shows significantly lower blood pressure. Which conclusion is best supported?

Answer: Daily walking appears to cause a reduction in blood pressure based on the randomized experiment.

Random assignment in a controlled experiment supports causal conclusions about the effect of walking on blood pressure within the study population.

A journalist reports that cities with more bicycle lanes have fewer traffic fatalities per capita. The journalist concludes that adding bicycle lanes reduces traffic deaths. What is the most significant flaw in this reasoning?

Answer: The data are observational; other differences between cities (e.g., population density, traffic laws) could explain the relationship.

Without controlling for other city-level differences, the correlation between bicycle lanes and lower fatalities may reflect confounding variables rather than a causal effect of the lanes.

Researchers randomly select 500 adults from a national registry, then randomly assign half to a new sleep therapy and half to standard care. The therapy group shows a significant improvement in sleep quality. To which group can the results be most validly generalized?

Answer: Adults similar to those in the national registry from which the sample was drawn

The random selection from a national registry allows generalization to the population represented by that registry; random assignment supports causal conclusions.

A researcher finds that students who participate in extracurricular activities have higher graduation rates than those who do not. The researcher claims participation in extracurriculars causes higher graduation rates. What is the most important limitation of this claim?

Answer: Students who participate in extracurriculars may differ from non-participants in motivation, family support, or other factors that also affect graduation.

Participation in extracurriculars is self-selected; students who join activities may already have characteristics (higher motivation, better support) that predict graduation regardless of participation.

A well-designed randomized controlled experiment finds that a specific tutoring program significantly raises math scores compared to a control group. Which of the following would be the most appropriate conclusion?

Answer: The tutoring program caused an increase in math scores for participants in this study.

A randomized experiment supports a causal claim within the study population, but generalizability and superiority over other programs require additional evidence.

A public health report notes that counties with higher rates of fast food restaurant density have higher obesity rates. An advocacy group concludes that fast food restaurants cause obesity. What is the primary weakness in this conclusion?

Answer: The county-level association is observational and may reflect socioeconomic or cultural confounders rather than a direct causal effect.

County-level observational data cannot establish causation; wealthier counties may have fewer fast food restaurants and also lower obesity rates for unrelated reasons.

A study randomly assigns 100 participants to write in a gratitude journal daily and 100 to write a neutral diary for 6 weeks, then measures happiness. The gratitude group scores significantly higher. What is the MOST valid conclusion?

Answer: The gratitude journaling practice caused higher happiness scores in this experiment.

Random assignment allows a causal conclusion that the gratitude journaling caused higher happiness scores within this experimental sample.