Funding for this research was provided by:
Familjen Erling-Perssons Stiftelse
Received: 23 December 2017
Accepted: 15 February 2018
First Online: 23 February 2018
Ethics approval and consent to participate
: This study has received ethical approval from the Regional Ethical Review Board in Stockholm, approval number: 2016/664–31/5 and 2017/7–31/1. Age-adapted information is given to all children and informed consent is obtained from parents/guardians for children under 15 years. Children over 15 year gives informed consent for their own participation in accordance with the Swedish law.
: Not applicable.
: The authors declare that they have no competing interests.
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