The target population of this survey was Cantonese-speaking population of Hong Kong of age 18 or above. To minimize sampling bias, the following sampling technique was adopted:

Telephone numbers were first drawn randomly from the residential telephone directories as “seed numbers”, from which another set of numbers was generated using the “plus/minus one/two” method, 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.

When telephone contact was successfully established with a target household, one person of age 18 or above was selected. If more than one qualified subject had been available, selection was made using the “next birthday rule” which selected the person who had his/her birthday next from all those present. Please refer to Appendix 1 for the demographic profile of the respondents.

Telephone interviews were carried out between 25 May and 31 May 2012. Data were collected by interviewers using a Computer Assisted Telephone Interviews (CATI) system under close supervision.

As shown from the detailed breakdown of the contact information, among the 23,057 telephone numbers sampled for the survey, 10,984 were confirmed ineligible, among them 1,112 were fax or data lines, 8,865 were invalid telephone numbers, 225 were call-forwarding numbers, while another 712 were non-residential numbers. Besides, 36 of them were invalidated due to special technological circumstances, while 34 cases were voided because no eligible respondents were available at the numbers provided.

Meanwhile, a total of 6,194 telephone numbers were invalidated since the research team could not confirm their eligibility. Among them 561 were busy lines, 4,307 were no-answer calls, 261 cases were diverted to answering devices while 91 were blocked. In addition, 317 cases were treated as ineligible because of language problems, 644 interviews were terminated before the screening question, while 13 cases were voided for other problems.

Of the remaining 5,879 eligible cases, 4,676 failed to complete the interview. Among them 24 rejected the interview immediately after their eligibility was confirmed, 4,588 were unfinished cases with appointment dates beyond the end of fieldwork period. Besides, 50 cases were incomplete due to unexpected termination of interviews, 14 were classified as miscellaneous due to other non-contact problems, and the remaining 1,203 were successful cases (Table 1).

To sum up, a total of 1,203 Hong Kong residents of age 18 or above were successfully interviewed in this survey. The overall response rate was 62.6% as shown in the following calculation. The standard error due to sampling was no more than 1.4 percentage points.

The data collected have been adjusted according to provisional figures obtained from the Census and Statistics Department regarding the gender-age distribution of the Hong Kong population at the end of 2011. All analyses in this report are based on the weighted data.

Statistical tests of “difference-of-proportions” and “difference-of-means” have been employed whenever applicable, in order to check for significant changes. Figures marked with single asterisk (*) denoted statistical significance at p=0.05 level whereas those with double asterisks (**) indicated that the variation has been tested to be statistically significant at p=0.01 level.

The researcher is aware that the POP Team is part of the University of Hong Kong, which is one of the institutions rated by the respondents. As a precaution to eliminate any possible bias due to desirability effect, all respondents were explicitly told at the beginning of the interview that the POP Team was an independent research team, and the respondents should simply report honestly what they felt.