Funding for this research was provided by:
The Norwegian Center for Child Behavioral Development
First Online: 15 February 2020
Compliance with Ethical Standards
: Dagfinn Mørkrid Thøgersen, Mette Elmose and Gunnar Bjørnebekk declare that they have no conflict of interest.
: Ethical approval for the study was given by The National Committee for Medical and Health Research Ethics (NEM) on 02.11.2010 and 02.10.2012 (Reference number 2010/497).
: Informed consent was obtained from all individual participants included in the study.
: All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.