Funding for this research was provided by:
Eesti Teadusagentuur (IUT 20-58, IUT34-4)
Text and Data Mining valid from 2018-07-11
Received: 30 January 2018
Accepted: 26 June 2018
First Online: 11 July 2018
Ethics approval and consent to participate
: The study was in accordance with the Declaration of Helsinki and approved by Research Ethics Committee of the University of Tartu (nr 255/M-11). Written informed consent was received from all schools, parents and students willing to participate.
: Not applicable
: The authors declare that they have no competing interests.
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