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Research Design返回


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 27 May and 3 June 2013. 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 21,908 telephone numbers sampled for the survey, 5,559 were confirmed ineligible, among them 1,760 were fax or data lines, 1,932 were invalid telephone numbers, 177 were call-forwarding numbers, while another 1,593 were non-residential numbers. Besides, 79 of them were invalidated due to special technological circumstances, while 18 cases were voided because no eligible respondents were available at the numbers provided.

 

Meanwhile, a total of 9,951 telephone numbers were invalidated since the research team could not confirm their eligibility. Among them 612 were busy lines, 7,556 were no-answer calls, 564 cases were diverted to answering devices while 57 were blocked. In addition, 549 cases were treated as ineligible because of language problems, 606 interviews were terminated before the screening question, while 7 cases were voided for other problems.

 

Of the remaining 6,398 eligible cases, 5,180 failed to complete the interview. Among them 10 rejected the interview immediately after their eligibility was confirmed, 5,122 were unfinished cases with appointment dates beyond the end of fieldwork period. Besides, 40 cases were incomplete due to unexpected termination of interviews, 8 were classified as miscellaneous due to other non-contact problems, and the remaining 1,218 were successful cases (Table 1).


Table 1    Breakdown of contact information of the survey

 

 

Frequency

Percentage

 

 

Telephone numbers’ ineligibility confirmed

 

5,559

 

25.4

Fax/data line

1,760

 

8.0

 

Invalid number

1,932

 

8.8

 

Call-forwarding/mobile/pager number

177

 

0.8

 

Non-residential number

1,593

 

7.3

 

Special technological circumstances

79

 

0.4

 

No eligible respondents

18

 

0.1

 

 

 

 

 

 

Telephone numbers’ or respondents’ eligibility not confirmed

 

9,951

 

45.4

Line busy

612

 

2.8

 

No answer

7,556

 

34.5

 

Answering device

564

 

2.6

 

Call-blocking

57

 

0.3

 

Language problem

549

 

2.5

 

Interview terminated before the screening question

606

 

2.8

 

Others

7

 

0.0

 

 

 

 

 

 

Telephone numbers’ eligibility confirmed, but failed to complete the interview

 

5,180

 

23.6

Household-level refusal

1

 

0.0

 

Known respondent refusal

9

 

0.0

 

Appointment date beyond the end of the fieldwork period

5,122

 

23.4

 

Partial interview

40

 

0.2

 

Miscellaneous

8

 

0.0

 

 

 

 

 

 

Successful cases

 

1,218

 

5.6

 

 

 

 

 

Total

 

21,908

 

100.0


To sum up, a total of 1,218 Hong Kong residents of age 18 or above were successfully interviewed in this survey. The overall response rate was 65.0% 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%
= [1,218 / (1,218 + 10 + 606 + 40)] 100%
= 65.0%



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 2012. 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.