The fragility index is a statistical measure used in clinical trials to assess the robustness of results. It quantifies the number of events that would need to change in order for the study's conclusion to be altered. A higher fragility index indicates that the study findings are more reliable, while a lower fragility index suggests that the results are more susceptible to small changes. Researchers often use the fragility index to evaluate the strength of evidence in a trial and to determine the validity of the study's conclusions.