2. (10 Points) Suppose you are trying to answer the following research question: "What is the effect of studying economics rather than social work on the salaries of university graduates?". a. What is the dependent variable and the independent variable in the question above? b. What plausible causal channel(s) runs directly from the treatment to the outcome? (i.e., what is the economic rationale for the two variables to be related, is there a reason one would cause the other) c. What are possible sources of selection bias in the raw comparison of outcomes by treatment status? Which way would you expect the bias to go and why