# Subgroup analysis (forest plots)

Source: https://onco.cc/terms/subgroup-analysis/  
OnCo record `subgroup-analysis` (Term). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

Splitting a trial's patients into groups (by age, sex, biomarker, region) to see whether the treatment worked the same in each. Shown as a forest plot. Genuine differences are rare and most striking subgroup results are noise, so they need confirmation.

## Summary

Trials are powered for the whole population, so subgroups have wide confidence intervals and, with a dozen subgroups, one will look different by chance; the proper test is for interaction, not for significance within each subgroup. Regulators have nonetheless used subgroups to restrict labels (PD-L1 cut-offs in gastro-oesophageal cancer, IMpassion130's PD-L1-positive population) and to question generalisability (regional differences in STARGLO, ex-US benefit in IMbrave050). Biologically plausible, pre-specified subgroups with a stratified randomisation carry more weight; a post-hoc TP53 wild-type subgroup with no interaction test (selinexor in endometrial cancer) needed its own trial.

## Fields

- Kind: Term
- Last checked: 2026-09-09
- Also known as: subgroup; subgroups; subgroup analysis; subgroup analyses; pre-specified subgroup; prespecified subgroup; subgroup effect; subgroup benefit; forest plot; forest plots; interaction test; test for interaction; heterogeneity of effect; consistent across subgroups; benefit was consistent; effect modification; biomarker subgroup; PD-L1 subgroup; high-volume subgroup; regional subgroup; Asian subgroup; Western subgroup; subgroup effects

## Sources

- Wikipedia: https://en.wikipedia.org/wiki/Subgroup_analysis
- Wikipedia: https://en.wikipedia.org/wiki/Subgroup_analysis

## Connected records

- terms: [Enrichment and biomarker-stratified designs](https://onco.cc/terms/biomarker-stratified-design/), [PD-L1 expression testing (22C3, SP142, SP263)](https://onco.cc/terms/pd-l1-testing/), [Pre-specified vs post-hoc analysis](https://onco.cc/terms/prespecified-vs-post-hoc/), [Statistical significance (P values, alpha, multiplicity)](https://onco.cc/terms/statistical-significance/), [Stratified randomisation, allocation concealment and minimisation](https://onco.cc/terms/stratified-randomisation/), [Why trials fail: underpowered, wrong endpoint, control arm drift, subgroup fishing, crossover](https://onco.cc/terms/trial-failure-modes/)
- fronts: [Drug Discovery Platforms](https://onco.cc/fronts/drug-discovery/)
- trials: [MAGNITUDE](https://onco.cc/trials/magnitude/), [RxPONDER (SWOG S1007)](https://onco.cc/trials/rxponder/), [Single-injection depot progesterone before breast surgery (Tata Memorial)](https://onco.cc/trials/progesterone-preop-tmh/)

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