Graphs are useful because of the way they:
a. facilitate interpretation and analysis of data

Randomization based on covariates is

A) not of practical importance since individuals are hardly ever assigned in this fashion. B) dependent on the covariances of the error term (serial correlation). C) a randomization in which the probability of assignment to the treatment group depends on one of more observable variables W. D) eliminates the omitted variable bias when using the difference estimator based on Yi = ?0 + ?1Xi + ui, where Y is the outcome variable and X is the treatment indicator.

Which of the following would be most likely to increase your opportunity cost of attending college?

a. a recession in the economy that made finding a job more difficult b. receiving a very attractive offer to start a job today that would permit you to earn about 50 percent more than you expected to make after graduation c. the retirement of your favorite professor under whom you hoped to study during the next semester d. information indicating that salaries were declining and that there were very few openings for college graduates in your field