Funding for this research was provided by:
Helse Sør-Øst RHF (150901)
Text and Data Mining valid from 2018-11-13
Received: 22 March 2018
Accepted: 31 October 2018
First Online: 13 November 2018
Ethics approval and consent to participate
: The research project has been approved by the Norwegian Data Protection Authority and the Norwegian Regional Committee for Medical and Health Research Ethics (REC South East). The unique personal identification number, assigned to all registered inhabitants in Norway, was used for linking data but subsequently deleted from the data file. Variables that could potentially be used for identifying individuals have either been deleted or recoded into broad categories, as stipulated by the Norwegian Data Protection Authority.
: Not applicable.
: The authors declares that they have no competing interests.
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