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Article History

Received: 1 September 2017

Accepted: 19 January 2018

First Online: 7 February 2018

Ethics approval and consent to participate

: The study was exempted from ethical review by the institutional review board of Seoul National University Hospital because the data originated from de-identified secondary data released by the National Health Insurance Service for research purposes. For the same reason, patient consent was not required for the present analysis.

: All authors gave their consent for publication of the study. No identifiable patient data are contained in this article.

: The authors declare that they have no competing interests.

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