Received: 5 October 2017
Accepted: 21 February 2018
First Online: 5 March 2018
Ethics approval and consent to participate
: The current study extracted data from publicly available online databases where no participation of individuals was involved. The need for ethics approval was waived by the Dutch Central Committee on Research Involving Human Subjects:ExternalRef removed
: Not applicable (no individually identifiable data are reported in this study).
: The authors declare that they have no competing interests.
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