Funding for this research was provided by:
Henning och Johan Throne-Holsts stiftelse för främjande av vetenskaplig forskning
Forskningsrådet i Norge (project number 228452)
Text and Data Mining valid from 2020-01-14
Received: 19 August 2019
Accepted: 4 January 2020
First Online: 14 January 2020
Ethics approval and consent to participate
: This study was conducted according to the guidelines laid down in the Declaration of Helsinki, and the Norwegian Center for Research Data approved all procedures involving human subjects. Parental written consent was obtained for 633 children.
: Not applicable.
: The authors declare that they have no competing interests.