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 will be randomly generated using known prefixes assigned to telecommunication services providers under the Numbering Plan provided by the Office of the Communications Authority (OFCA). Invalid numbers will then be eliminated according to computer and manual dialing records to produce the final 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 22 May and 5 June 2015. 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 32,014 telephone numbers sampled for the survey, 8,196 were confirmed ineligible, among them 972 were fax or data lines, 6,143 were invalid telephone numbers, 223 were call-forwarding numbers, while another 744 were non-residential numbers. Besides, 86 of them were invalidated due to special technological circumstances, while 28 cases were voided because no eligible respondents were available at the numbers provided.

Meanwhile, a total of 14,303 telephone numbers were invalidated since the research team could not confirm their eligibility. Among them 1144 were busy lines, 11,397 were no-answer calls, 752 cases were diverted to answering devices while 41 were blocked. In addition, 392 cases were treated as ineligible because of language problems, 562 interviews were terminated before the screening question, while 15 cases were voided for other problems.

Of the remaining 8,314 eligible cases, 7,113 failed to complete the interview. Among them 17 rejected the interview immediately after their eligibility was confirmed, 8,229 were unfinished cases with appointment dates beyond the end of fieldwork period. Besides, 51 cases were incomplete due to unexpected termination of interviews, 17 were classified as miscellaneous due to other non-contact problems, and the remaining 1,201 were successful cases (Table 1).

To sum up, a total of 1,201 Hong Kong residents of age 18 or above were successfully interviewed in this survey. The overall response rate was 65.6% 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 in 2014 year-end and the educational attainment (highest level attended) distribution collected in the 2011 Census. 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.