Statistical Significance in Trauma Research: Too Unstable to Trust?

To evaluate the stability of statistical findings in the fracture care literature based on minor changes in event rates and to determine the utility of applying both the Fragility Index (FI) and Fragility Quotient (FQ) to comparative orthopaedic trauma trials.

All fracture care studies from 1991 to 2013 in the Journal of Bone and Joint Surgery and the Journal of Orthopaedic Trauma were screened. The FI was determined by altering the number of reported outcome events, a single event at time, until a reversal of statistical significance was determined. The associated FQ was determined by dividing the FI by the total sample size.

Of the 4040 studies evaluated, 198 comparative studies met inclusion criteria with a reported 253 primary and 522 secondary outcome events. There were 118 randomized controlled trials and 80 retrospective comparative studies. Of the 775 total outcome events, 235 were initially reported as significant. The median FI for the entire study was only 5 with an associated FQ of 0.046. This represents just 3.8% of the total study population.

The robustness of comparative trials in the orthopaedic trauma literature may not be as stable as previously thought with only a few event reversals required to alter trial significance. We therefore recommend triple reporting of a P value, FI, and FQ to aid in the evaluation and interpretation of statistical stability and quantitative significance in comparative orthopaedic trauma trials.