Funding for this research was provided by:
Text and Data Mining valid from 2020-02-14
Received: 5 December 2019
Accepted: 15 January 2020
First Online: 14 February 2020
Compliance with ethical guidelines
: J. C. Katthagen, E. Hesse, H. Lill, B. Schliemann, A. Ellwein, M.J. Raschke and J. Imrecke declare that they have no competing interests.
: The study protocol was approved by the local ethics committee of the Medizinische Hochschule Hannover (1840–2013) and complied with the principles of the Declaration of Helsinki.