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Contributors The present study was done as a part of a PhD project at Martin Luther University Halle-Wittenberg by SK.
Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Competing interests The authors have specified any conflict of interest to be involved.
Ethics approval The study protocol was submitted to the Ethics Committee of the Medical Faculty of the Martin Luther University of Halle-Wittenberg and positively assessed (processing No. 2017-16).
Provenance and peer review Not commissioned; externally peer reviewed.
Patient consent for publication Not required.
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