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Table 1 Key issues when assessing subgroup treatment effects

From: Osteoarthritis subpopulations and implications for clinical trial design

Prognostic factors are not necessarily treatment effect modifiers
Post hoc subgroup effects in trials should be regarded as unreliable unless they can be replicated in dedicated trials or meta-analyses
When subgroup analysis is predefined in a trial, randomisation should be stratified by subgroup and the power should be adjusted to the smallest subgroup
Testing for interaction effects in trials is more robust than subgroup analysis, but needs a well-powered study depending on the expected size of the interaction effect
The number of subgroups should be limited to a minimum to avoid multiple testing
Combining trials for meta-analysis has the potential to search for subgroup effects. For reliable subgroup meta-analysis, individual trials have to supply subgroup effects and use stratified treatment randomization by subgroup, or supply the distribution of prognostic variables over the treatment arms in the subgroup
Meta-analysis using individual patient data is a powerful method and the gold standard for assessing subgroup-treatment interaction effects