Received: 16 April 2018
Accepted: 10 October 2018
First Online: 19 October 2018
Ethics approval and consent to participate
: Data managed and obtained under the regulation of the Federal Statistics Act (FSA) of 1992. Secondary use of the SHS data was approved by the Swiss Federal Statistical Office (contract number 160512) and secondary use of the Nat-ABBE was approved by the board of Nat-ABBE data management directors from all participating universities.
: Not applicable.
: The authors declare that they have no competing interests.
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