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. 2020 May 22:M20-2567. doi: 10.7326/M20-2567

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This article is made available via the PMC Open Access Subset for unrestricted re-use for research, analyses, and text and data mining through PubMed Central. Acknowledgement of the original source shall include a notice similar to the following: "© 2020 American College of Physicians. Some rights reserved. This work permits non-commercial use, distribution, and reproduction in any medium, provided the original author and source are credited." These permissions are granted for the duration of the COVID-19 pandemic or until permissions are revoked in writing. Upon expiration of these permissions, PMC is granted a perpetual license to make this article available via PMC and Europe PMC, consistent with existing copyright protections.

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Figure. — Definitions of and relationship among FE, PF, and TIL.

For consistency, we calculated FE from data provided in the original work rather than presenting the data in the units chosen by the authors. PF and fit factor are synonyms. FE = filtration efficiency; PF = protection factor; TIL = total inward leakage.