Discontinuity Design for a Merit Scholarship

A researcher conducts a study to measure the impact of joining a competitive debate team on students' final grades in their government class. The study finds that students who voluntarily joined the debate team had significantly higher final grades than students who did not. The researcher concludes that participation in debate directly causes academic improvement in government class. Which statement best analyzes the primary flaw in this conclusion?

Analyzing a Workplace Study

Evaluating a Tutoring Program Study

Evaluating a Music Program's Impact

A study observes that towns with a higher number of firefighters per capita also tend to have more property damage from fires. Based on this strong positive correlation, the most logical conclusion is that having more firefighters on staff leads to an increase in fire-related property damage.

Each 'Study Finding' below describes a correlation between two variables that might be mistaken for a direct causal link. Match each finding to the most likely 'Hidden Factor' that explains the relationship.

A study observes that individuals who regularly attend the gym have a lower incidence of a specific chronic illness compared to those who do not. However, it's possible that people who choose to go to the gym are also more likely to have healthier diets, and this dietary difference could be the real reason for their better health outcomes. In this analysis, the 'healthier diet' is an example of a(n) ___________ variable, making it difficult to determine the true health benefit of gym attendance alone.

Analyzing a City's Crime Reduction Program

Evaluating a Corporate Training Program

A study finds that children who own high-end, technologically advanced bicycles tend to have higher scores on standardized science tests. The researchers conclude that interacting with the complex mechanics and materials of these bicycles stimulates an interest and aptitude for science. What is the most likely confounding variable that challenges this conclusion?