Read the paper at https://journals.lww.com/epidem/Fulltext/2021/05000/Generalizability_of…
Generalizability of Subgroup Effects

Generalizability methods are increasingly used to make inferences about the effect of interventions in target populations using a study sample. Most existing methods to generalize effects from sample to population rely on the assumption that subgroup-specific effects generalize directly. However, researchers may be concerned that in fact subgroup-specific effects differ between sample and population.