Received: 27 January 2017
Accepted: 21 July 2017
First Online: 14 August 2017
Ethics approval and consent to participate
: This study complies with the Declaration of Helsinki. All participants gave written consent. MONICA is covered by ethical permission from the Regional Ethics Committee in Umeå in 2013 (2013/97-31).
: Not applicable.
: The authors declare that they have no competing interests.
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