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