Text and Data Mining valid from 2019-01-25
Received: 24 October 2018
Accepted: 18 January 2019
First Online: 25 January 2019
Compliance with ethical standards
: The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.