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 30 May and 12 June 2006. 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 16,030 telephone numbers sampled for the survey, 6,168 were confirmed ineligible, among them 767 were fax or data lines, 4,319 were invalid telephone numbers, 80 were call-forwarding numbers, while another 746 were non-residential numbers. Besides, 164 of them were invalidated due to special technological circumstances, while 92 cases were voided because no eligible respondents were available at the numbers provided.


Meanwhile, a total of 4,300 telephone numbers were invalidated since the research team could not confirm their eligibility. Among them 317 were busy lines, 2,416 were no-answer calls, 56 cases were diverted to answering devices while 248 were blocked. In addition, 261 cases were treated as ineligible because of language problems, 942 interviews were terminated before the screening question, while 60 cases were voided for other problems.


Of the remaining 5,562 eligible cases, 4,053 failed to complete the interview. Among them 32 rejected the interview immediately after their eligibility was confirmed, 3,867 were unfinished cases with appointment dates beyond the end of fieldwork period. Besides, 81 cases were incomplete due to unexpected termination of interviews, 73 were classified as miscellaneous due to other non-contact problems, and the remaining 1,509 were successful cases (Table 1).

Table 1 - Breakdown of contact information of the survey
   Frequency  Percentage
  Respondents' ineligibility confirmed  6,168   38.5 
  Fax/ data line  767   4.8 
  Invalid number  4,319   26.9 
  Call-forwarding/ mobile/ pager number  80   0.5 
  Non-residential number  746   4.7 
  Special technological difficulties  164   1.0 
  No eligible respondents  92   0.6 
  Respondents' eligibility not confirmed  4,300   26.8 
  Line busy  317   2.0 
  No answer  2,416   15.1 
  Answering device  56   0.3 
  Call-blocking  248   1.5 
  Language problem  261   1.6 
  Interview terminated before the screening question  942   5.9 
  Others  60   0.4 
  Respondents' eligibility confirmed, but failed to complete the interview  4,053   25.3 
  Household-level refusal  7   0.0 
  Known respondent refusal  25   0.2 
  Appointment date beyond the fieldwork period  3,867   24.1 
  Partial interview  81   0.5 
  Miscellaneous  73   0.5 
  Successful cases  1,509   9.4 
  Total  16,030   100.0 

To sum up, a total of 1,509 Hong Kong residents of age 18 or above were successfully interviewed in this survey. The overall response rate was 58.9% as shown in the following calculation. The standard error due to sampling was no more than 1.3 percentage points.

Table 2 - Calculation of overall response rate

   Overall response rate
= [Successful cases / (Successful cases + Refusal cases + Incomplete cases)] * 100%
= [1,509 / (1,509 + 32 + 1,023)] * 100%
= 58.9%

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 2005. 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 universities 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.