Research Method返回

 

Research Method

 

 

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 15 June 2009. 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 15,402 telephone numbers sampled for the survey, 6,869 were confirmed ineligible, among them 666 were fax or data lines, 5,198 were invalid telephone numbers, 171 were call-forwarding numbers, while another 755 were non-residential numbers. Besides, 45 of them were invalidated due to special technological circumstances, while 34 cases were voided because no eligible respondents were available at the numbers provided.

Meanwhile, a total of 3,839 telephone numbers were invalidated since the research team could not confirm their eligibility. Among them 235 were busy lines, 2,651 were no-answer calls, 77 cases were diverted to answering devices while 54 were blocked. In addition, 222 cases were treated as ineligible because of language problems, 559 interviews were terminated before the screening question, while 41 cases were voided for other problems.

Of the remaining 4,694 eligible cases, 3,493 failed to complete the interview. Among them 25 rejected the interview immediately after their eligibility was confirmed, 3,225 were unfinished cases with appointment dates beyond the end of fieldwork period. Besides, 55 cases were incomplete due to unexpected termination of interviews, 186 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

 

6,869

 

44.6%

Fax/data line

666

 

4.3%

 

Invalid number

5,198

 

33.7%

 

Call-forwarding/mobile/pager number

171

 

1.1%

 

Non-residential number

755

 

4.9%

 

Special technological circumstances

45

 

0.3%

 

No eligible respondents

34

 

0.2%

 

 

 

 

 

 

Telephone numbers' or respondents' eligibility not confirmed

 

3,839

 

24.9%

Line busy

235

 

1.5%

 

No answer

2,651

 

17.2%

 

Answering device

77

 

0.5%

 

Call-blocking

54

 

0.4%

 

Language problem

222

 

1.4%

 

Interview terminated before the screening question

559

 

3.6%

 

Others

41

 

0.3%

 

 

 

 

 

 

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

 

3,493

 

22.7%

Household-level refusal

5

 

0.0%

 

Known respondent refusal

20

 

0.1%

 

Appointment date beyond the end of the fieldwork period

3,225

 

20.9%

 

Partial interview

55

 

0.4%

 

Miscellaneous

186

 

1.2%

 

 

 

 

 

 

Successful cases

 

1,201

 

7.8%

 

 

 

 

 

Total

 

15,402

 

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 65. 2% 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 + 25 + 559 + 55)] 100%
= 65.2%

 

 

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 2008. 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.