git:20260226.1632f40 to git:20260430.0124814

4 added, 2 removed. Audit A to A.

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name: designing-experiments

- description: Selects the appropriate quasi-experimental method (DiD, ITS, SC) based on data structure and research questions. Use when the user is unsure which method to apply.

+ description: Design experiments and quasi-experiments before analysis. Use when choosing study design, treatment/control structure, outcomes, assumptions, or which of DiD, ITS, synthetic control, or regression discontinuity fits the research question. For fitting models or estimating effects on existing data, use performing-causal-analysis instead.

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# Designing Experiments

- Helps select the appropriate causal inference method.

+ Helps choose and specify a research design before data analysis starts. This skill owns study-design decisions: what is treated, what is compared, what outcome is measured, which assumptions are required, and which design is defensible.

+ It does not fit causal models, estimate treatment effects, or interpret fitted model output from existing data.

## 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).