Subgroup Effect: 5 Tips to Judge Trustworthiness .

Subgroup analyses help determine whether a treatment works differently across distinct patient groups, but their credibility can vary widely. A tibial fracture trial comparing reamed and unreamed nails raised questions when overall results showed no advantage, yet a subgroup of open fractures appeared to benefit from unreamed fixation. Assessing such findings requires checking whether subgroups were predefined, whether the trial was well designed, whether results could be due to chance, and whether a biological rationale supports the pattern. In this case, the subgroup hypothesis was specified early, the trial was rigorous, the statistical signal was unlikely to be random, and a plausible explanation existed, making the subgroup effect more believable.