Background: The fragility index has been proposed as a metric to evaluate the robustness of statistically significant findings in randomized controlled trials. It measures the number of events that a trial result relies on to maintain statistical significance. This study examines the robustness of statistically significant results from randomized controlled trials in the plastic surgery literature.
Methods: A systematic literature search of the 15 highest impact plastic surgery journals was conducted to identify randomized controlled trials published between 2000 and 2017 that reported a statistically significant dichotomous outcome (p < 0.05). The fragility index of each study was calculated using Fisher's exact test. Multiple linear regression was used to determine trial characteristics associated with the fragility index.
Results: The 90 eligible randomized controlled trials had a median sample size of 73.5 patients (25th to 75th percentile, 50 to 115) and a median of 20 events (25th to 75th percentile, 11 to 33.5) for the chosen outcome. The median fragility index was 1 (25th to 75th percentile, 0 to 4), indicating that statistical significance would be lost in half of the randomized controlled trials if a single patient had a change in event status. The fragility index was 0 in 24 of 90 (27 percent) randomized controlled trials, meaning the outcome immediately lost statistical significance on recalculation of the p value using Fisher's exact test.
Conclusions: The results of randomized controlled trials in plastic surgery demonstrate substantial fragility, as statistically significant results were found to hinge on a small number of events. The fragility index offers an intuitive and simple metric to complement the p value and determine the confidence in the results of randomized controlled trials.