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Article History

Received: 16 June 2017

Accepted: 19 January 2018

First Online: 30 January 2018

Ethics approval and consent to participate

: The study was approved by the Research Ethics Committee of the University of Tartu (decision no. 235/T-12). With the questionnaire the study subjects received a cover letter explaining the aim and the methods (including data protection) of the study. The cover letter explained that the participation in the study (returning at least partially filled questionnaire) would be considered to constitute informed consent. Additional written consent was not obtained.

: Not applicable.

: The authors declare that they have no competing interests.

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