The Fragility Index used to verify medical breakthroughs is mathematically broken and cannot be calculated for many valid trials.
Medical researchers use the Fragility Index to decide if a drug's success is a fluke or a real discovery. This widely accepted metric is fundamentally incomplete because its underlying math fails in common data scenarios. When the index cannot be calculated, scientists often ignore the result or interpret it incorrectly. This flaw puts the reliability of numerous clinical trials into question. It means the tool designed to make science more stable is itself a fragile piece of software.
Mathematical incompleteness of the fragility index
research_square · rs-9315771
Abstract Background The Fragility Index (FI) is intended to quantify how many outcome changes would be required to convert a statistically significant two-arm trial result into a non-significant one. For a metric defined on valid 2×2 trial tables, mathematical completeness means that a finite numeric value is obtainable for every valid input in its intended domain. This study evaluated whether the Fragility Index satisfies that property. Methods FI was analyzed as defined: baseline significance