Received: 19 February 2018
Accepted: 28 December 2018
First Online: 14 January 2019
Ethics approval and consent to participate
: The study was approved by the Singapore National Health Care Group, Domain Specific Review Board (DSRB). Verbal consent was approved by the ethics board and obtained from all participants.
: Not applicable.
: FM-R is a member of the editorial board (Associated Editor) of BMC public health. All other authors declare that they have no competing interests.
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