This was a random telephone survey conducted by interviewers under close supervision. To minimize sampling bias, telephone numbers were first drawn randomly from the residential telephone directories as "seed numbers", from which another set of numbers was generated by computer, in order to capture the unlisted numbers. Duplicated numbers were then filtered, and the remaining numbers were mixed in random order to produce the final telephone sample.
The target population of this survey was Hong Kong residents aged 18 or above who spoke Cantonese. When telephone contact was successfully established with a target household, one person of age 18 or above who spoke Cantonese was selected. If more than one subject had been available, selection was made using the "next birthday rule" which selected the person who had his/her birthday next.
Telephone interviews were conducted during the period of 5 to 12 March, 2013. A total of 1,009 Hong Kong residents of age 18 or above were successfully interviewed. As shown from the calculation in Appendix 1, the overall response rate of this survey was 68.4% (Table 1), and the standard sampling error for percentages based on this sample was less than 1.6 percentage points. In other words, the sampling error for all percentages using the total sample was less than plus/minus 3.1 percentage points at 95% confidence level.