2.2. Design of survey experiment
For the survey experiment, three information blocks were designed as background information for the participants before indicating their vaccination acceptance (Messages on the three strategies used in the survey experiment.Combining the three blocks, there were eight groups (2 × 2 × 2) of information that were different from each other in full-factorial design. The participants were first asked for their age, sex, and COVID-19 vaccination status, and then randomly assigned to one of the eight groups, stratified by age and sex. The randomization was performed using the built-in “randomizer” function in the widely-used Qualtrics (Provo, UT, USA) online survey platform, where the respondents have equal chance to be assigned to each one of the eight groups in the following survey experiment. For those who received at least one dose of vaccine, they were asked “under this context, when you have not received COVID-19 vaccine, would you receive the COVID-19 vaccine earlier than you actual did? (Yes/No)” after being shown the three information blocks. For those who did not receive any COVID-19 vaccine, they were asked “under this context, would you receive the COVID-19 vaccine in recent days? (Yes/No)” after the three information blocks. Six public health professionals and 10 adult members of the general public, belonging to different ages and occupations identified from our participant panel, who have similar cultural backgrounds as our study sample, were invited to review an assessment of the information blocks and survey experiment to improve its face validity and ensure study participants understood the questions and how to respond to them.