Funding for this research was provided by:
Beat Drugs Fund, Narcotics Division, Security Bureau of Hong Kong SAR (160051)
Received: 21 January 2020
Accepted: 12 April 2020
First Online: 22 April 2020
Ethics approval and consent to participate
: All procedures performed in studies involving human participants were in accordance with the ethical standards of the Survey and Behavioral Research Ethics Committee of the Chinese University of Hong Kong and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. The ethics committee approved obtaining verbal instead of written informed consent. Fieldworkers signed a form pledging that the participants had been fully informed about the study.
: Not applicable.
: The authors declare that they have no conflict of interest.