Funding for this research was provided by:
This work was partly funded by a grant from the Ministry of Social Affairs and Health, Finland.
Received: 31 July 2017
Accepted: 15 January 2018
First Online: 9 February 2018
Ethics approval and consent to participate
: The research plan was approved by the Institutional Review Board (IRB) of National Institute for Health and Welfare (THL) (IRB 00007085, FWA 00014588). The study participation was voluntary and parents of the pupils were able to deny participation in advance.
: Not applicable.
: The authors declare that they have no competing interests.
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