The data in ECONMATH were obtained on students from a large university course in introductory microeconomics. For this problem, we are interested in two variables: score, which is the final course score, and econhs, which is a binary variable indicating whether a student took an economics course in high school.

(i) How many students are in the sample? How many students report taking an economics course in high school?

(ii) Find the average of score for those students who did take a high school economics class. How does it compare with the average of score for those who did not?

(iii) Do the findings in part (ii) necessarily tell you anything about the causal effect of taking high school economics on college course peformance? Explain.

(iv) If you want to obtain a good causal estimate of the effect of taking a high school economics course using the difference in averages, what experiment would you run?