We randomly select half of econometrics students to attend extra office hours with a faculty member. At the end of the semester, we find no evidence that this affects the final exam scores. The Dean argues that this means faculty members are ineffective teachers. I argue that spillover effects led to these small estimates because.
A. Students who attended the extra office hours passed their knowledge onto others.
B. Not everyone who was selected to attend the extra office hours did so.
C. Some people who were not selected nonetheless demanded and received extra office hours.
D. We screwed up the randomization and were more likely to give extra office hours to students with lower midterm grades.
Answer: A. Students who attended the extra office hours passed their knowledge onto others.