Funding for this research was provided by:
Universitetet i Agder
The Eckbo foundation https://www.eckbos-legat.no/
Text and Data Mining valid from 2019-01-03
Received: 20 July 2018
Accepted: 12 December 2018
First Online: 3 January 2019
Ethics approval and consent to participate
: The study is conducted in accordance with the Helsinki Declaration of 1975 as revised in 1983. The Norwegian Centre for Research Data evaluated and approved the study (ExternalRef removed). Informed consent from all participating parents was obtained upon registration.
: Not applicable.
: The authors declare that they have no competing interests.
: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.