A New York Times editorial (“Public vs. Private Schools,” 2006) cited a finding by the U.S. Department of Education that standardized test scores were significantly higher among students in private schools than among students in public schools. 

a. What are the researchers suggesting with respect to causality? 

b. How could this correlation be explained by reversing the direction of hypothesized causality? Be specific. 

c. How might a third variable account for this correlation? Be specific. Note that there are many possible “third” variables.