Model-Free Survival Fragility Restores Robustness in Clinical Trials Reporting the Survival-Inferred Fragility Index

Abstract

The Survival-Inferred Fragility Index (SIFI), introduced in 2020 and now applied to first-line metastatic renal cell carcinoma immunotherapy trials, extends the fragility concept into time-to-event oncology outcomes by iteratively reassigning long-surviving patients between trial arms until statistical significance is lost. This reassignment rule is model-dependent: the choice of which survivors to move and in what order embeds distributional assumptions about the survival tail, so SIFI values are path-dependent and therefore have limited cross-trial comparability. The Survival Fragility Quotient, derived from the Cox regression z-statistic and paired with the Survival Robustness Quotient on the neutrality boundary, provides a model-free survival fragility measure without iterative reassignment, requires only the reported hazard ratio and its confidence interval, and completes the p–fr–nb triplet for time-to-event outcomes. Oncology randomized trial reporting should adopt the model-free pair to support cross-trial comparability of the quality of survival evidence.