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 local working class of age 18-64 who are MPF members. 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 July 14 to 25, 2014. 1,020 respondents were successfully interviewed. The effective response rate was 80.4%, and the standard sampling error for percentages based on this sample was less than 1.6 percentage points. In other words, the maximum sampling error for percentages was less than plus/minus 3.1 percentage points at 95% confidence level.