Suppose We Are Studying the Effects of Expanded Income Supplement

Multiple Choice

Suppose we are studying the effects of expanded income supplement for senior citizens on their health. We use the two-group, to-period differences-in-differences setup, with working-age citizens as our control group. Which of the following is a key assumption for the validity of this identification strategy?

A) In the absence of the intervention, the average health outcomes would be the same for both groups.
B) Before the intervention, the average health outcomes were the same for both groups.
C) After the intervention, the average health trends would be the same for both groups.
D) In the absence of the intervention, the average health trends would be the same for both groups.