Research DesignBack

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 13 June 2011. 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 23,604 telephone numbers sampled for the survey, 11,759 were confirmed ineligible, among them 1,147 were fax or data lines, 9,139 were invalid telephone numbers, 193 were call-forwarding numbers, while another 1,147 were non-residential numbers. Besides, 94 of them were invalidated due to special technological circumstances, while 39 cases were voided because no eligible respondents were available at the numbers provided.

Meanwhile, a total of 5,842 telephone numbers were invalidated since the research team could not confirm their eligibility. Among them 413 were busy lines, 4,213 were no-answer calls, 223 cases were diverted to answering devices while 111 were blocked. In addition, 330 cases were treated as ineligible because of language problems, 504 interviews were terminated before the screening question, while 48 cases were voided for other problems.

Of the remaining 6,003 eligible cases, 4,802 failed to complete the interview. Among them 22 rejected the interview immediately after their eligibility was confirmed, 4,679 were unfinished cases with appointment dates beyond the end of fieldwork period. Besides, 54 cases were incomplete due to unexpected termination of interviews, 47 were classified as miscellaneous due to other non-contact problems, and the remaining 1,201 were successful cases (Table 1).

Table 1 Breakdown of contact information of the survey

	Frequency		Percentage
Telephone numbers』 ineligibility confirmed		11,759		49.8
Fax/data line	1,147		4.9
Invalid number	9,139		38.7
Call-forwarding/mobile/pager number	193		0.8
Non-residential number	1,147		4.9
Special technological circumstances	94		0.4
No eligible respondents	39		0.2

Telephone numbers』 or respondents』 eligibility not confirmed		5,842		24.8
Line busy	413		1.7
No answer	4,213		17.8
Answering device	223		0.9
Call-blocking	111		0.5
Language problem	330		1.4
Interview terminated before the screening question	504		2.1
Others	48		0.2

Telephone numbers』 eligibility confirmed, but failed to complete the interview		4,802		20.3
Household-level refusal	4		0.0
Known respondent refusal	18		0.1
Appointment date beyond the end of the fieldwork period	4,679		19.8
Partial interview	54		0.2
Miscellaneous	47		0.2

Successful cases		1,201		5.1

Total		23,604		100.0

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 67.4% as shown in the following calculation. The standard error due to sampling was no more than 1.4 percentage points.

Table 2 Calculation of overall response rate

Overall response rate
= [Successful cases / (Successful cases + Refusal cases + Incomplete cases)] 100%
= [1,201 / (1,201 + 22 + 504 + 54)] 100%
= 67.4%

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 2010. 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.