Missing data methods for intensive care unit SOFA scores in electronic health records studies: results from a Monte Carlo simulation.

Missing data cause problems through decreasing sample size and the potential for introducing bias. We tested four missing data methods on the Sequential Organ Failure Assessment (SOFA) score, an intensive care research severity adjuster. Simulation study using 2015-2017 electronic health record data, where the complete dataset was sampled, missing SOFA score elements imposed and performance examined of four missing data methods - complete case analysis, median imputation, zero imputation (recommended by SOFA score creators) and multiple imputation (MI) - on the outcome of in-hospital mortality. MI performed well, whereas other methods introduced varying amounts of bias or decreased sample size. We recommend using MI in analyses where SOFA score component values are missing in administrative data research.