Research MethodBack

Post-"July 1 Demonstration" Opinion Survey on BL23 and the POP regular tracking poll were both random telephone surveys 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 both surveys 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.

Post-"July 1 Demonstration" Opinion Survey on BL23 was conducted between 4 and 5 July 2003. A total of 1,160 Cantonese-speaking Hong Kong citizens aged 18 or above were successfully interviewed. As shown from the calculation below, the overall response rate of this survey was 71.0% (Table 1), and the standard sampling error for percentages based on this sample was less than 1.5 percentage points. In other words, the sampling error for all percentages was less than plus/minus 3 percentage points at 95% confidence level.

* Including "partial interview" and "interview terminated before the screening question"
^ Including "household-level refusal" and "known respondent refusal"

As shown in Table 3, among the 7,538 telephone numbers sampled for the survey, 1,977 were confirmed to be ineligible, among them 349 were fax or data lines, 1,132 were invalid telephone numbers, 39 were call-forwarding numbers, while another 254 were non-residential numbers. Besides, 87 of them were invalidated due to special technological reasons, while 116 cases were voided because target respondents were unavailable at the numbers provided.

Meanwhile, a total of 3,316 telephone numbers were invalidated before the research team could confirm their eligibility. Among them 174 were busy lines and 2,261 were no-answer calls after making a maximum of 5 times' recalls. Forty-six cases were diverted to answering devices while another 50 were blocked. Moreover, 196 cases were treated as unsuccessful because of language problems, while 417 interviews were terminated before the screening question. Besides, 172 cases were voided for other problems.

On the other hand, 1,085 cases failed to complete the interview. Among them 5 were rejected at the household level, another 4 rejected the interview immediately after their eligibility was confirmed, 977 were unfinished cases with appointment dates beyond the end of fieldwork period. Besides, 48 cases were incomplete due to unexpected termination of interviews, 51 were classified as miscellaneous due to other non-contact problems, and the remaining 1,160 were successful cases (Table 3).

As for the POP tracking poll, the survey was conducted between 2 and 4 July 2003. A total of 1,046 Cantonese-speaking Hong Kong citizens aged 18 or above were successfully interviewed. As shown from the calculation below, the overall response rate of this survey was 66.3% (Table 2), and the standard sampling error for percentages based on this sample was less than 1.5 percentage points. In other words, the sampling error for all percentages was less than plus/minus 3 percentage points at 95% confidence level.

* Including "partial interview" and "interview terminated before the screening question"
^ Including "household-level refusal" and "known respondent refusal"

As shown in Table 3, among the 6,426 telephone numbers sampled for the survey, 1,876 were confirmed to be ineligible, among them 321 were fax or data lines, 1,050 were invalid telephone numbers, 40 were call-forwarding numbers, while another 260 were non-residential numbers. Besides, 102 of them were invalidated due to special technological reasons, while 103 cases were voided because target respondents were unavailable at the numbers provided.

Meanwhile, a total of 2,141 telephone numbers were invalidated before the research team could confirm their eligibility. Among them 95 were busy lines and 1,187 were no-answer calls after making a maximum of 5 times' recalls. Fifty-two cases were diverted to answering devices while another 55 were blocked. Moreover, 126 cases were treated as unsuccessful because of language problems, while 436 interviews were terminated before the screening question. Besides, 190 cases were voided for other problems.

On the other hand, 1,363 cases failed to complete the interview. Among them 8 were rejected at the household level, another 10 rejected the interview immediately after their eligibility was confirmed, 1,184 were unfinished cases with appointment dates beyond the end of fieldwork period. Besides, 77 cases were incomplete due to unexpected termination of interviews, 84 were classified as miscellaneous due to other non-contact problems, and the remaining 1,046 were successful cases (Table 3).