Research DesignBack


 

This was a random telephone survey conducted by telephone interviewers under close supervision. To minimize sampling bias, 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.

 
 

The target population of this survey was Cantonese-speaking population of Hong Kong aged 18 or above. 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 conducted during the period of 1 to 7 November 2005. A total of 1,003 Cantonese-speaking Hong Kong citizens aged 18 or above were successfully interviewed. The overall response rate of this survey was 64.6% (Table 2), and the standard sampling error for percentages based on this sample was less than 1.6 percentage points. In other words, the sampling error for all percentages was less than plus/minus 3.2 percentage points at 95% confidence level.


Table 1 - Breakdown of contact information of the survey
   Frequency  Percentage
  Respondents' ineligibility confirmed  3,244   44.5 
  Fax/ data line  409   5.6 
  Invalid number  2,268   31.1 
  Call-forwarding/ mobile/ pager number  50   0.7 
  Non-residential number  355   4.9 
  Special technological difficulties  117   1.6 
  No eligible respondents  45   0.6 
 
  Respondents' eligibility not confirmed  2,279   31.3 
  Line busy  124   1.7 
  No answer  928   12.7 
  Answering device  30   0.4 
  Call-blocking  326   4.5 
  Language problem  305   4.2 
  Interview terminated before the screening question  534   7.3 
  Others  32   0.4 
 
  Respondents' eligibility confirmed, but failed to complete the interview  763   10.5 
  Household-level refusal  2   0.0 
  Known respondent refusal  7   0.1 
  Appointment date beyond the fieldwork period  626   8.6 
  Partial interview  7   0.1 
  Miscellaneous  121   1.7 
 
  Successful cases  1,003   13.8 
 
  Total  7,289   100.0 

Table 2 - Calculation of overall response rate

   Overall response rate
= [ Successful cases / (Successful cases + Refusal cases* + Incomplete cases^) ]
= [ 1,003 / ( 1,003 + 541 + 9 ) ]
= 64.6%
* Including "partial interview" and "interview terminated before the screening question"
^ Including "household-level refusal" and "known respondent refusal"