# Designing Experiments > 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. Use when this capability is needed. - Skill: `tomevault-io/designing-experiments` (Agent Skill, multi-file: 2 files) - Install (CLI): `npx skillmds@latest add tomevault-io/designing-experiments` - Raw SKILL.md: https://api.skillmd.com/api/skills/tomevault-io/designing-experiments/raw - Safety review: pending - Works with: Claude Code, Claude.ai, OpenAI Codex - Category: Research & Search - Author: tomevault-io (https://skillmd.com/u/tomevault-io) - Updated: 2026-09-17 - Page: https://skillmd.com/skills/tomevault-io/designing-experiments --- # 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). --- > Converted and distributed by [TomeVault](https://tomevault.io/claim/pymc-labs) — claim your Tome and manage your conversions.