Received: 26 March 2019
Accepted: 30 September 2019
First Online: 24 October 2019
Ethics approval and consent to participate
: The study was approved by the Danish Data Protection Agency (ref. 2007-58-0015, int. ref.: GEH-2014-018), and data were made available in a way that individuals could not be identified. Approval from an ethics committee is not required for retrospective register-based studies in Denmark.The data that support the findings of this study are available from third party (DST, Danmark Statistik) but restrictions apply to the availability of these data and they are not publicly available. Data are only available upon reasonable request and through permission from DST.
: Not applicable.
: The authors declare that they have no competing interests.