designing-experiments

1# Designing Experiments
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3Helps 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, which validation or recovery experiment should follow a failed scientific experiment, and which design is defensible.
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5It does not fit causal models, estimate treatment effects, interpret fitted model output from existing data, or debug software/build failures.
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7## Decision Framework
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91.  **Control Group?**
10    *   **Yes**: Go to Step 2.
11    *   **No**: Consider **Interrupted Time Series (ITS)**.
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132.  **Unit Structure?**
14    *   **Single Treated Unit**:
15        *   With multiple controls: **Synthetic Control (SC)**.
16        *   No controls: **ITS**.
17    *   **Multiple Treated Units**:
18        *   With control group: **Difference-in-Differences (DiD)**.
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203.  **Time Structure?**
21    *   **Panel Data** (Multiple units over time): Required for DiD and SC.
22    *   **Time Series** (Single unit over time): Required for ITS.
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24## Method Quick Reference
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26*   **Difference-in-Differences (DiD)**: Compares trend changes between treated and control groups. Assumes **Parallel Trends**.
27*   **Interrupted Time Series (ITS)**: Analyzes trend/level change for a single unit after intervention. Assumes **Trend Continuity**.
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