Telephone interviews were conducted by interviewers under close supervision. All data were collected by our interviewers using a Computer Assisted Telephone Interview (CATI) system which allowed real-time data capture and consolidation. To ensure data quality, on top of on-site supervision, voice recording, screen capturing and camera surveillance were used to monitor the interviewers' performance.
The target population of this survey is Cantonese-speaking citizens in Hong Kong of age 18 to 55 years. If more than one eligible subject had been available, the one who had his/her birthday next was selected.
The survey was conducted during the period of January 14 to 27, 2014. 512 respondents were successfully interviewed. The effective response rate was 77.1%, and the standard sampling error for percentages based on this sample was less than 2.2 percentage points. In other words, the maximum sampling error for percentages was less than plus/minus 4.4 percentage points at 95% confidence level.
