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 female citizens in Hong Kong of age 18 to 45 years. If more than one eligible subject had been available, the one who had her birthday next was selected.
The survey was conducted during the period of April 16 to 25, 2013. 503 respondents were successfully interviewed. The effective response rate was 53.4%, 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 4.5 percentage points at 95% confidence level.