Research Design^


 
 

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.

 
 

Telephone interviews were carried out from 1830 to 2230 hours between 25 February and 1 March 2002. 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, amongst the 6,989 telephone numbers sampled for the survey, 843 were found to be invalid lines, 2,558 were non-contacts, including busy lines and no answer, another 261 were business lines, 473 were fax lines or with answering machines while 114 were classified as miscellaneous due to other non-contact problems. Of the 2,740 valid contacts, the numbers of refusals (without knowing whether target respondents were qualified or not), disqualified and unfinished cases with appointment dates beyond the end of fieldwork period were 621, 265 and 410 respectively. Besides, 15 cases were incomplete due to unexpected termination of interviews, 400 have language and other problems, and the remaining 1,029 were successful cases.

 
 
Table 1. Breakdown of contact information of the survey
   Frequency  Percentage
 Telephone numbers attempted  6,989   
 Invalid numbers  843  
 Busy / no answer  2,558  
 Business lines  261  
 Fax / answering machine  473  
 Miscellaneous  114  
     
 Valid contacts  2,740   100.0% 
 Refusal  621  22.7%
 Failed to qualify  265  9.7%
 Appointment  410  15.0%
 Incomplete  15  0.5%
 Other problems  400  14.6%
 Successful  1,029  37.6%
 
 

To sum up, a total of 1,029 Hong Kong residents aged 18 or above were successfully interviewed in the survey. The effective response rate was 61.8% as shown in the following calculation. The standard error due to sampling was no more than 1.6 percentage points.

 
 
Table 2 Calculation of effective response rate

   Effective response rate
= [Successful cases / (Successful cases + Refusal cases +Incomplete cases)] 100%
= [1,029 / (1,029 + 621+ 15)] 100%
= 61.8%
 
 

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.

 
 

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.