. 2021 Jun 14;9(6):649. doi: 10.3390/vaccines9060649
© 2021 by the authors.
Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).
Figure 1.
The flow chart of propensity score matching.