Research MethodBack

 

 

 

 

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 26 June and 4 July 2008. 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 13,808 telephone numbers sampled for the survey, 5,663 were confirmed ineligible, among them 615 were fax or data lines, 4,139 were invalid telephone numbers, 118 were call-forwarding numbers, while another 675 were non-residential numbers. Besides, 62 of them were invalidated due to special technological circumstances, while 54 cases were voided because no eligible respondents were available at the numbers provided.

Meanwhile, a total of 3,571 telephone numbers were invalidated since the research team could not confirm their eligibility. Among them 151 were busy lines, 2,110 were no-answer calls, 52 cases were diverted to answering devices while 55 were blocked. In addition, 263 cases were treated as ineligible because of language problems, 571 interviews were terminated before the screening question, while 369 cases were voided for other problems.

Of the remaining 4,574 eligible cases, 3,361 failed to complete the interview. Among them 20 rejected the interview immediately after their eligibility was confirmed, 2,548 were unfinished cases with appointment dates beyond the end of fieldwork period. Besides, 48 cases were incomplete due to unexpected termination of interviews, 745 were classified as miscellaneous due to other non-contact problems, and the remaining 1,213 were successful cases (Table 1).

 

 

 

Table 1 - Breakdown of contact information of the survey

 
Frequency
Percentage
Telephone numbers' ineligibility confirmed
5,663
41.0%
Fax/ data line
615
4.5%
Invalid number
4,139
30.0%
Call-forwarding/ mobile/ pager number
118
0.9%
Non-residential number
675
4.9%
Special technological circumstances
62
0.4%
No eligible respondents
54
0.4%
 
 
 
Telephone numbers' or respondents' eligibility not confirmed
3,571
25.9%
Line busy
151
1.1%
No answer
2,110
15.3%
Answering device
52
0.4%
Call-blocking
55
0.4%
Language problem
263
1.9%
Interview terminated before the screening question
571
4.1%
Others
369
2.7%
 
 
 
Telephone numbers' eligibility confirmed, but failed to complete the interview
3,361
24.3%
Household-level refusal
12
0.1%
Known respondent refusal
8
0.1%
Appointment date beyond the end of the fieldwork period
2548
18.5%
Partial interview
48
0.3%
Miscellaneous
745
5.4%
 
 
 
Successful cases
1,213
8.8%
 
 
 
Total
13,808
100.0%

 

 

To sum up, a total of 1,213 Hong Kong residents of age 18 or above were successfully interviewed in this survey.? The overall response rate was 65.5% 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%
= [1,213 / (1,213 + 20 + 619)] 100%
= 65.5%

 

 

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 2007. 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 double asterisks (**) indicated that the variation has been tested to be statistically significant at p=0.01 level, whereas those with single asterisk (*) denoted statistical significance at p=0.05 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.