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. 2019 May 11;21(6):e13482. doi: 10.2196/13482

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©Zhongxing Zhang, Christian Cajochen, Ramin Khatami. Originally published in the Journal of Medical Internet Research (http://www.jmir.org), 11.05.2019.

This is an open-access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work, first published in the Journal of Medical Internet Research, is properly cited. The complete bibliographic information, a link to the original publication on http://www.jmir.org/, as well as this copyright and license information must be included.

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The distribution of adjusted mid-point of sleep on free days (MSFsc) in our subjects (N=49,573). The red, green, and blue colors mark the early, intermediate, and late types using arbitrary cut-offs of <3 am, 3-5 am, and >5 am, respectively. h: hours.