Difference-in-Differences · Policy Evaluation
Difference-in-Differences: The 2×2 Design
DID compares change over time in a treated group with change over time in a comparison group.
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The big picture: Difference-in-Differences: The 2×2 Design
What changed more in the treated group than in the comparison group?
Why a policy analyst should care
Difference-in-differences removes stable group differences and common time changes, focusing the causal argument on whether untreated trends would have remained parallel.
Follow the idea from the opening question to a practical decision. These are the conceptual moves this module will develop:
1 Question What changed more in the treated group than in the comparison group?
2 Explore ER admissions around Medicaid expansion
3 Formalize The difference-in-differences estimand
4 Transfer Defend a 2×2 policy evaluation
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