You evaluate the effect of a micro-finance program on income by comparing areas that chose to receive the program to those that did not, both before and after the program was introduced. What do you need to determine to ensure that your comparison is valid:
A. Income levels looked similar in the program and non-program areas in the pre-treatment period.
B. Income levels looked similar in the program and non-program areas in the post-treatment period.
C. The pre-period trend in income between the program and non-program is constant over time
D. The post-period trend in income between the program and non-program areas is constant over time
Answer: C. The pre-period trend in income between the program and non-program is constant over time