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 4 and 18 June 2010. 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 16,133 telephone numbers sampled for the survey, 7,448 were confirmed ineligible, among them 764 were fax or data lines, 5,805 were invalid telephone numbers, 113 were call-forwarding numbers, while another 677 were non-residential numbers. Besides, 39 of them were invalidated due to special technological circumstances, while 50 cases were voided because no eligible respondents were available at the numbers provided.

Meanwhile, a total of 4,327 telephone numbers were invalidated since the research team could not confirm their eligibility. Among them 292 were busy lines, 2,960 were no-answer calls, 113 cases were diverted to answering devices while 90 were blocked. In addition, 297 cases were treated as ineligible because of language problems, 565 interviews were terminated before the screening question, while 10 cases were voided for other problems.

Of the remaining 4,358 eligible cases, 3,150 failed to complete the interview. Among them 34 rejected the interview immediately after their eligibility was confirmed, 3,006 were unfinished cases with appointment dates beyond the end of fieldwork period. Besides, 62 cases were incomplete due to unexpected termination of interviews, 48 were classified as miscellaneous due to other non-contact problems, and the remaining 1,208 were successful cases (Table 1).

Table 1 Breakdown of contact information of the survey

	Frequency		Percentage
Telephone numbers' ineligibility confirmed		7,448		46.2
Fax/data line	764		4.7
Invalid number	5,805		36.0
Call-forwarding/mobile/pager number	113		0.7
Non-residential number	677		4.2
Special technological circumstances	39		0.2
No eligible respondents	50		0.3

Telephone numbers' or respondents' eligibility not confirmed		4,327		26.8
Line busy	292		1.8
No answer	2,960		18.3
Answering device	113		0.7
Call-blocking	90		0.6
Language problem	297		1.8
Interview terminated before the screening question	565		3.5
Others	10		0.1

Telephone numbers' eligibility confirmed, but failed to complete the interview		3,150		19.5
Household-level refusal	9		0.1
Known respondent refusal	25		0.2
Appointment date beyond the end of the fieldwork period	3,006		18.6
Partial interview	62		0.4
Miscellaneous	48		0.3

Successful cases		1,208		7.5

Total		16,133		100.0

To sum up, a total of 1,208 Hong Kong residents of age 18 or above were successfully interviewed in this survey. The overall response rate was 64.6% 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%
= [1,208 / (1,208 + 34 + 565 + 62)] 100%
= 64.6%

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 2009. 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.