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 23 and 30 March 2005. 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 12,166 telephone numbers sampled for the survey, 4,309 were confirmed ineligible, among them 581 were fax or data lines, 2,683 were invalid telephone numbers, 63 were call-forwarding numbers, while another 617 were non-residential numbers. Besides, 212 of them were invalidated due to special technological circumstances, while 153 cases were voided because no eligible respondents were available at the numbers provided.


Meanwhile, a total of 4,090 telephone numbers were invalidated since the research team could not confirm their eligibility. Among them 281 were busy lines, 2,173 were no-answer calls, 63 cases were diverted to answering devices while 273 were blocked. In addition, 390 cases were treated as ineligible because of language problems, 900 interviews were terminated before the screening question, while 10 cases were voided for other problems.


Of the remaining 3,767 eligible cases, 2,250 failed to complete the interview. Among them 18 rejected the interview immediately after their eligibility was confirmed, 2,150 were unfinished cases with appointment dates beyond the end of fieldwork period. Besides, 73 cases were incomplete due to unexpected termination of interviews, 9 were classified as miscellaneous due to other non-contact problems, and the remaining 1,517 were successful cases (Table 1).

Table 1 - Breakdown of contact information of the survey
   Frequency  Percentage
  Respondents' ineligibility confirmed  4,309   35.5 
  Fax/ data line  581   4.8 
  Invalid number  2,683   22.1 
  Call-forwarding/ mobile/ pager number  63   0.5 
  Non-residential number  617   5.1 
  Special technological difficulties  212   1.7 
  No eligible respondents  153   1.3 
  Respondents' eligibility not confirmed  4,090   33.6 
  Line busy  281   2.3 
  No answer  2,173   17.9 
  Answering device  63   0.5 
  Call-blocking  273   2.2 
  Language problem  390   3.2 
  Interview terminated before the screening question  900   7.4 
  Others  10   0.1 
  Respondents' eligibility confirmed, but failed to complete the interview  2,250   18.5 
  Household-level refusal  4   0.0 
  Known respondent refusal  14   0.1 
  Appointment date beyond the fieldwork period  2,150   17.7 
  Partial interview  73   0.6 
  Miscellaneous  9   0.1 
  Successful cases  1,517   12.5 
  Total  12,166   100.0 

To sum up, a total of 1,517 Hong Kong residents of age 18 or above were successfully interviewed in the survey. The effective response rate was 60.5% 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%
= [1,517 / (1,517 + 18 + 973)] * 100%
= 60.5%

The data collected have been adjusted according to the age and gender distributions of the Hong Kong population as reported in the 2001 Population Census. 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.