Funding for this research was provided by:
Ministry of Education and Research
Received: 4 June 2018
Accepted: 26 August 2019
First Online: 18 September 2019
Ethics approval and consent to participate
: For the 2012-data the Regional Committee for Medical and Health Research (REC) South-East Norway (Ref. number 2010/3326) reviewed and approved the study. Participating was voluntary, and consent was given by responding to the questionnaire. For the 2016-data approval was obtained from the Norwegian Social Science Data Services (NSD; project number 45723). All participants received information regarding the purpose of the study; they were assured that the digital questionnaires were to be treated in confidence and that no participants could be identified in the published material. Their written consent to participate in the study was given at the start of the survey.
: Not applicable.
: The authors declare that they have no competing interests.