Research MethodBack

This "Opinion survey on Hong Kong Harbour Fest" was a random telephone survey conducted by telephone interviewers under close supervision. 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 a random order to produce the final telephone sample.
The target population of this survey was Hong Kong residents of age 15 or above. When telephone contact was successfully established with a target household, one person aged 15 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.
The survey was conducted between 27 November and 10 December 2003. A total of 2,026 Hong Kong residents aged 15 or above were successfully interviewed. As shown from Table 1 below, the overall response rate of this survey was calculated to be 57.0%. The standard sampling error for percentages based on this sample was less than 1.1 percentage points. In other words, the sampling error for all percentages based on the full sample was less than plus/minus 2.2 percentage points at 95% confidence level.
Table 1 Calculation of overall response rate

   Overall response rate
= [Successful cases / (Successful cases + Refusal cases^ +Incomplete cases*)] 100%
= [2,026 / (2,026 + 31+ 1,499)] 100%
= 57.0%
^ Including "household-level refusal" (14 cases) and "known respondent refusal" (17 cases).
* Including "partial interview"(125 cases) and "interview terminated before the screening question" (1,374 cases).
As shown in Table 2, among the 10,286 telephone numbers sampled for the survey, 3,639 were confirmed to be ineligible, among them 609 were fax or data lines, 2,110 were invalid telephone numbers, 36 were call-forwarding numbers, while another 583 were non-residential numbers. Besides, 180 of them were invalidated due to special technological reasons, i.e. the number did not match exactly with the one shown in the computer system, while 121 cases were voided because target respondents were unavailable at the numbers provided.
Meanwhile, a total of 3,847 telephone numbers were invalidated before the research team could confirm their eligibility. Among them 136 were busy lines and 1,358 were no-answer calls after making a maximum of 5 times' recalls. Forty-three cases were diverted to answering devices while another 400 were blocked. Moreover, 108 cases were treated as unsuccessful because of language problems, while 1,374 interviews were terminated before the screening question. Besides, 428 cases were voided for other problems.
On the other hand, 774 cases failed to complete the interview. Among them 14 were rejected at the household level, another 17 rejected the interview immediately after their eligibility was confirmed, 618 were unfinished cases with appointment dates beyond the end of fieldwork period. Besides, 125 cases were incomplete due to unexpected termination of interviews, and the remaining 2,026 were successful cases (Table 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.
Table 2 Detailed breakdown of contact information
   Frequency  Percentage
  Respondents' ineligibility confirmed  3,639   35.3 
  Fax/ data line  609   5.9 
  Invalid number  2,110   20.5 
  Call-forwarding/ mobile/ pager number  36   0.3 
  Non-residential number  583   5.7 
  Special technological difficulties  180   1.7 
  No eligible respondents  121   1.2 
  Respondents' eligibility not confirmed  3,847   37.4 
  Line busy  136   1.3 
  No answer  1,358   13.2 
  Answering device  43   0.4 
  Call-blocking  400   3.9 
  Language problem  108   1.0 
  Interview terminated before the screening question  1,374   13.4 
  Others  428   4.2 
  Respondents' eligibility confirmed, but failed to complete the interview  774   7.5 
  Household-level refusal  14   0.1 
  Known respondent refusal  17   0.2 
  Appointment date beyond the fieldwork period  618   6.0 
  Partial interview  125   1.2 
  Successful cases  2,026   19.7 
  Total  1,0286   100.0