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An introduction to propensity score matching methods
Anesth Pain Med 2016;11(2):130-48
Published online April 30, 2016
© 2016 The Korean Society of Anesthesiologists.

Dong Kyu Lee
Department of Anesthesiology and Pain Medicine, Korea University Guro Hospital, Seoul, Korea
Correspondence to: Dong Kyu Lee, M.D., Ph.D., Department of Anesthesiology and Pain Medicine, Korea University Guro Hospital, 148, Gurodong-ro, Guro-gu, Seoul 08308, Korea. Tel: 82-2-2626-1437, Fax: 82-2-2626-1438, E-mail:
Received January 18, 2016; Revised February 2, 2016; Accepted February 22, 2016.
cc This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License ( which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Propensity score matching method (PSM) is widely used in observational study to reduce selection bias. Observational study lacks randomization, hence, statistical inferences without bias adjustments usually include observed or unobserved effects of covariates. If a subject with specific characteristics has a higher chance to be selected for a specific treatment, the characteristics have a possible effect on statistical results. PSM is the method for controlling covariate imbalance that produces the selection bias. In this paper, we introduce the basic concepts of PSM and simplified methods of PSM process. However, PSM is a rapidly developing statistical area with many limitations and some disadvantages. These points are described in the concluding section to emphasize the importance of considering the various features of PSM in the study design.

Key Words : Observational study, Propensity score matching method, Selection bias

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