Research Method返回

 

Research Method

 
 

The target population of this survey was Cantonese-speaking population of Hong Kong aged 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 aged 18 or above was selected. If more than one 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 from 1830 to 2230 hours between 27 February and 6 March 2004. 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 11,225 telephone numbers sampled for the survey, 3,951 were confirmed ineligible, among them 557 were fax or data lines, 2,084 were invalid telephone numbers, 94 were call-forwarding numbers, while another 765 were non-residential numbers. Besides, 264 of them were invalidated due to special technological circumstances, while 187 cases were voided because no eligible respondents were available at the numbers provided.

 
 

Meanwhile, a total of 3,898 telephone numbers were invalidated since the research team could not confirm their eligibility. Among them 211 were busy lines, 2,051 were no-answer calls, 53 cases were diverted to answering devices while 304 were blocked. In addition, 353 cases were treated as ineligible because of language problems, 901 interviews were terminated before the screening question, while 25 cases were voided for other problems.

 
 

Of the remaining 3,376 eligible cases, 1,863 failed to complete the interview. Among them 14 rejected the interview immediately after their eligibility was confirmed, 1,744 were unfinished cases with appointment dates beyond the end of fieldwork period. Besides, 84 cases were incomplete due to unexpected termination of interviews, 21 were classified as miscellaneous due to other non-contact problems, and the remaining 1,513 were successful cases (Table 1).

 
 
Table 1 - Breakdown of contact information of the survey
   Frequency  Percentage
  Respondents' ineligibility confirmed  3,951   35.3 
  Fax/ data line  557   5.0 
  Invalid number  2,084   18.6 
  Call-forwarding/ mobile/ pager number  94   0.8 
  Non-residential number  765   6.8 
  Special technological difficulties  264   2.4 
  No eligible respondents  187   1.7 
 
  Respondents' eligibility not confirmed  3,898   34.7 
  Line busy  211   1.9 
  No answer  2,051   18.3 
  Answering device  53   0.5 
  Call-blocking  304   2.7 
  Language problem  353   3.1 
  Interview terminated before the screening question  901   8.0 
  Others  25   0.2 
 
  Respondents' eligibility confirmed, but failed to complete the interview  1,863   16.5 
  Household-level refusal  9   0.1 
  Known respondent refusal  5   0.0 
  Appointment date beyond the fieldwork period  1,744   15.5 
  Partial interview  84   0.7 
  Miscellaneous  21   0.2 
 
  Successful cases  1,513   13.5 
 
  Total  11,225   100.0 
 
 

To sum up, a total of 1,513 Hong Kong residents aged 18 or above were successfully interviewed in the survey. The effective response rate was 60.2% 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%
= [1,513 / (1,513 + 14 + 985)] * 100%
= 60.2%
 
 

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.