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skills/subgroup-analysis/SKILL.md

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+---
+name: subgroup-analysis
+description: "Conduct subgroup analyses to examine effect moderation. Use when: (1) Testing pre-specified moderators, (2) Exploring heterogeneity, (3) Identifying differential effects, (4) Meta-analysis synthesis."
+allowed-tools: Read, Write, Bash
+version: 1.0.0
+---
+
+# Subgroup Analysis Skill
+
+## Purpose
+Examine whether effects differ across subgroups of participants or studies.
+
+## Planning Subgroup Analyses
+
+**Pre-Specify:**
+- Which subgroups (age, sex, severity)
+- Rationale for each
+- Statistical approach
+
+**Limit Number:**
+- Too many = Type I error inflation
+- Focus on theoretically important
+- Correct for multiple comparisons
+
+## Subgroup Analysis Methods
+
+**1. Interaction Tests**
+- Test group × subgroup interaction
+- More powerful than separate analyses
+
+**2. Stratified Analysis**
+- Separate analysis per subgroup
+- Compare effect sizes
+
+**3. Meta-Regression**
+- Continuous moderators
+- Multiple moderators simultaneously
+
+## Interpretation Cautions
+
+**Observational Nature:**
+- Subgroups not randomized
+- Confounding possible
+- Generate hypotheses, don't confirm
+
+**Multiple Testing:**
+- Adjust alpha (Bonferroni)
+- Or report as exploratory
+
+**Example:**
+"Pre-specified subgroup analysis showed larger effects in younger participants (<50 years, d=0.68) versus older (≥50 years, d=0.34), interaction p=.02."
+
+---
+**Version:** 1.0.0