Received: 20 April 2018
Accepted: 24 April 2019
First Online: 10 May 2019
Ethics approval and consent to participate
: All data were anonymized and publicly available; therefore, this study was deemed exempt from ethical approval by the ethics committee of Imperial College.
: Filippos Filippidis is an Associate Editor for BMC Public Health. The rest of the authors declare that they have no competing interests.
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