812 Review Article Page 1 of 39 Propensity score matching with R: conventional methods and new features Qin-Yu Zhao1#, Jing-Chao Luo2#, Ying Su2, Yi-Jie Zhang2, Guo-Wei Tu2, Zhe Luo3 1College of Engineering and Computer Science, Australian National University, Canberra, ACT, Australia; 2Department of Critical Care Medicine, Zhongshan Hospital, Fudan University, Shanghai, China; 3Department of Critical Care Medicine, Xiamen Branch, Zhongshan Hospital, Fudan University, Xiamen, China Contributions: (I) Conception and design: QY Zhao, JC Luo; (II) Administrative support: GW Tu; (III) Provision of study materials or patients: GW Tu, Z Luo; (IV) Collection and assembly of data: QY Zhao; (V) Data analysis and interpretation: QY Zhao; (VI) Manuscript writing: All authors; (VII) Final approval of manuscript: All authors. #These authors contributed equally to this work. Correspondence to: Guo-Wei Tu. Department of Critical Care Medicine, Zhongshan Hospital, Fudan University, Shanghai 200032, China. Email:
[email protected]; Zhe Luo. Department of Critical Care Medicine, Xiamen Branch, Zhongshan Hospital, Fudan University, Xiamen 361015, China. Email:
[email protected]. Abstract: It is increasingly important to accurately and comprehensively estimate the effects of particular clinical treatments. Although randomization is the current gold standard, randomized controlled trials (RCTs) are often limited in practice due to ethical and cost issues. Observational studies have also attracted a great deal of attention as, quite often, large historical datasets are available for these kinds of studies. However, observational studies also have their drawbacks, mainly including the systematic differences in baseline covariates, which relate to outcomes between treatment and control groups that can potentially bias results.