The fragility index is one way to look at the significance of the findings of a clinical trial.

Requirement: data set with a dichotomous outcome and a p value < 0.05


Derivation of the fragility index:

(1) Redetermine the p value after changing one "positive" result to a "negative" one.

(2) Repeat until the p value is > 0.05.

(3) The fragility index is the number of results that were changed.



A small fragility index says that only a few results needed to be different to get a different p value.


Limitations and observations:

(1) The fragility index depends on the p value, which can have limited significance.

(2) In some studies the underlying problem is poor experimental design with the studies being underpowered.

(3) The number of results lost to follow-up become significant if the fragility index is small, since the missing results could have impacted the p value if they had been included.

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