Received: 15 November 2019
Accepted: 9 June 2020
First Online: 15 June 2020
Ethics approval and consent to participate
: The study was approved by the South-East Regional Committees for Medical and Health Research Ethics in Norway (approval number: 2014/1278). Data were used under licence for the current study.
: Not applicable.
: The authors declare that they have no competing interests.