The residential division of prism's high-speed internet service uses one advertising agency, while its commercial division uses another. two analysts, andy and brad, are asked to test the effectiveness of the two agencies. andy proposes an a/b test that compares the click-through rates per ad of the two agencies. brad proposes a difference-in-difference test in which the budgets for both agencies are increased by 50%, and the percentage changes in the click-through rates are compared. true or false: brad's difference-in-differences estimator is more likely to suffer from "leakage" than andy's.

Suppose that a major city’s main thoroughfare, which is also an interstate highway, will be completely closed to traffic for two years, from january 2014 to december 2015, for reconstruction at a cost of $535 million. if the construction company were to keep the highway open for traffic during construction, the highway reconstruction project would take much longer and be more expensive. suppose that construction would take four years if the highway were kept open, at a total cost of $800 million. the state department of transportation had to make its decision in 2014, one year before the start of construction (so that the first payment was one year away). so the department of transportation had the following choices: (i) close the highway during construction, at an annual cost of $267.5 million per year for two years. (ii) keep the highway open during construction, at an annual cost of $200 million per year for four years. now suppose the interest rate is 80%. calculate the present value of the costs incurred under each plan.