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Article History

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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