Evaluating Statistical Claims: Observational Studies and Experiments Flashcards
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A study randomly assigns 120 employees to a four-day workweek and 120 to a five-day workweek for 3 months, then measures productivity and job satisfaction. The four-day group scores higher on both. What conclusion is best supported?
Answer: A four-day workweek caused higher productivity and job satisfaction compared to a five-day workweek in this experiment.
Random assignment supports the causal conclusion that the four-day workweek caused higher productivity and satisfaction in this study population and timeframe.
An observational study finds that children who own more books at home have higher reading scores. A librarian claims that donating books to low-income homes will raise reading scores. What is the most significant concern with this conclusion?
Answer: Homes with more books may also have parents who read more to their children, higher parental education, and more verbal interaction—confounding the effect of books alone.
The number of books in the home is strongly correlated with parental education and reading habits, which are the true drivers of reading scores in this observational data.
A controlled experiment randomly assigns 500 overweight adults to either a low-carbohydrate diet or a low-fat diet for 6 months. The low-carb group loses significantly more weight. A nutritionist says: 'This proves low-carb diets are superior for everyone.' What is the most important limitation of this claim?
Answer: The study participants may not represent all overweight adults, so the results may not apply to everyone.
Even with random assignment supporting a causal claim, the sample's characteristics determine generalizability; 'everyone' is too broad based on a single trial.
A school researcher observes that students who sit in the front rows earn higher grades than those who sit in the back. The researcher recommends assigning all struggling students to front seats. What is the primary flaw in this recommendation?
Answer: Students who choose front seats may be more motivated and engaged regardless of where they sit, creating self-selection confounding.
Students who voluntarily sit in front are likely more motivated and attentive; moving struggling students to the front may not replicate the effect if motivation is the real driver.
A randomized study finds that patients who received cognitive behavioral therapy (CBT) alongside medication improved more than patients who received medication alone. The study recruited patients from mental health clinics in three states. To which population can the findings be most validly generalized?
Answer: Patients with similar diagnoses receiving care at comparable mental health clinics
The random selection from mental health clinics in three states supports generalization to patients at similar clinics; random assignment supports the causal claim.
A study observes that high school students who commute by bicycle have lower rates of obesity than those who commute by car or bus. A city planner concludes that promoting bicycle commuting will reduce student obesity. Which evidence would most strengthen this causal claim?
Answer: A randomized experiment that provides free bicycles to a randomly selected group of students and compares obesity rates to a control group after one year
Only a randomized experiment (providing bicycles to randomly selected students) can control for self-selection bias and establish that bicycle commuting causes lower obesity.
An observational study finds that countries with stricter gun laws have lower rates of gun violence. A policy analyst concludes that adopting stricter gun laws will reduce gun violence. What is the most important limitation?
Answer: Countries with stricter gun laws may differ in culture, income inequality, policing, and other factors that independently affect gun violence rates.
Countries differ in many ways beyond gun laws; the correlation may reflect deeper cultural, economic, or social differences that jointly determine both gun law stringency and violence rates.