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. 2021 Jun 29;12:704316. doi: 10.3389/fphar.2021.704316

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Copyright © 2021 Chen, Huang, Peng, Tsai, Huang, Yu and Chien.

This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

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Incidence of acute exacerbation of chronic obstructive pulmonary disease within one year among the patients in the PIFR group and control group. AE: acute exacerbation. RR: relative risk. CI: confidence intervals.