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To the Editor The study by Dr Le Manach and colleagues1 compared differences in hospital mortality between patients undergoing hip fracture surgery and elective total hip replacement. A population matched for age, sex, and preoperative comorbidities to patients who underwent the 2 operations was created using a multivariable logistic model and a greedy matching algorithm with a 1:1 ratio. This matching model is useful for adjusting the patients’ baseline characteristics and controlling selection biases in a retrospective study, but it carries the significant assumption of no unmeasured confounders. That is, all important known factors that can affect measured outcomes must be measured and taken into account in the matching model.
Xue FS, Liu GP, Li RP. Hip Fracture Surgery vs Elective Total Hip Replacement. JAMA. 2016;315(9):941. doi:10.1001/jama.2015.17858