Received: 28 December 2017
Accepted: 19 June 2018
First Online: 15 August 2018
Ethics approval and consent to participate
: The study is based on secondary data from more than 2000 surveys. Written consent was obtained from all the organizations to which the surveys belong to. Data was anonymized before starting the analyses.
: Not applicable
: The authors declare that they have no competing interests.
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