Designing Experiments

Helps select the appropriate causal inference method.

Decision Framework

1. Control Group?

   • Yes: Go to Step 2.
   • No: Consider Interrupted Time Series (ITS).

2. Unit Structure?

   • Single Treated Unit:
     • With multiple controls: Synthetic Control (SC).
     • No controls: ITS.
   • Multiple Treated Units:
     • With control group: Difference-in-Differences (DiD).

3. Time Structure?

   • Panel Data (Multiple units over time): Required for DiD and SC.
   • Time Series (Single unit over time): Required for ITS.

Method Quick Reference

• Difference-in-Differences (DiD): Compares trend changes between treated and control groups. Assumes Parallel Trends.
• Interrupted Time Series (ITS): Analyzes trend/level change for a single unit after intervention. Assumes Trend Continuity.
• Synthetic Control (SC): Constructs a synthetic counterfactual from weighted control units. Assumes Convex Hull (treated unit within range of controls).