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Article History

Received: 18 December 2017

Accepted: 16 October 2018

First Online: 8 November 2018

Ethics approval and consent to participate

: The Institutional Review Board (IRB) of Asan Medical Center determined that this study was exempt from IRB review (approval number: S2016–0015). Prior to enrollment, we explained the objectives and processes of this study to the participants and obtained verbal informed consent from them with verbal and written consents. We obtained verbal informed consent rather than written consent, because this study presented no more than minimal risk of harm to participants and the only record linking the participants and the study would be the consent document.

: Not available.

: The authors declare that they have no competing interest. The datasets used and analysed during the current study are available from the corresponding author on reasonable request.

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