Received: 11 April 2019
Accepted: 3 June 2019
First Online: 12 June 2019
Ethics approval and consent to participate
: The study was approved by the Danish Data Protection Agency (j-nr. 2007-58-0015/local.j.nr. GEH-2014-015 I-Suite nr: 02,733). In Denmark, ethical approval is not required for register-based studies.
: Not applicable.
: The authors declare that they have no competing interests.