A professor decides to run an experiment to measure the effect of time pressure on scores. He gives each of the 400 students in their course the same test but some students have 90 minutes to complete the test while others have 120 minutes. Suppose that the professor works in a school where there are 6 classes for each year cohort. As a first step, the professor decided to give 90 minutes to all the students in classes from 1 to 3 and give 120 minutes to classes from 4 to 6

a) is this the right procedure to retrieve the causal effect? Discuss your answer

b) What is the selection problem, and why a Randomised Control Trial can fix this problem? Explain.

c) What are the challenges behind the design and implementation of an RCT?