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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).
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Table 1 - Breakdown of contact information of the
survey
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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% |
| |
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|
| 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% |
| |
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| 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% |
| |
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| Successful cases |
1,213 |
8.8% |
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| Total |
13,808 |
100.0% |
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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.
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