Experimental Design Details
As with the previous experiment, we define as “vaccinated individuals” Japanese people who received the two COVID-19 vaccinations and had the intention to receive the additional vaccine as of January-February 2022. We also define as “unvaccinated individuals” those who did not receive or intend to receive the vaccine as of January-February 2022.
First, through MyVoice.com Ltd., an online survey company, we conduct a follow-up screening survey for those who joined the previous main experiment and still register with the survey company (736 vaccinated individuals and 694 unvaccinated individuals) and ascertain their current vaccination status. To obtain a total of 800 vaccinated individuals and 800 unvaccinated individuals for a follow-up main experiment, we also conduct the follow-up screening survey for those who joined only the previous screening survey (if the target number is still not reached, we will collect new respondents).
Second, we sample 800 vaccinated individuals and 800 unvaccinated ones from the respondents of the follow-up screening survey, and conduct the follow-up main experiment with financially incentivized dictator games, where we randomly assign the participants to either of the five groups described above. In the experiment part, we first present, as priming, the COVID-19-related questions, including whether they have received the COVID-19 vaccine. We then present a dictator game five times as in the procedure above. In each game, participants are given an endowment of 100 Japanese yen in addition to the participation fee. They are also asked to decide how much of the 100 yen they give to a paired other person. Participants are informed that the paired person is not participating in this same survey, that the participant solely determine the allocation, that they are the only one who can give a share of the money to the paired person, and that after the experiment, one of the five experimental responses will be randomly selected to carry out that allocation.
Before and after the experiment, we set questions to ascertain psychological and behavioral economic characteristics, health status, and the COVID-19-related behavioral characteristics and attitudes. Concretely, the COVID-19-related questions include attitudes toward the COVID-19-related policies (Balancing infectious disease control and socio-economic activities, vaccination certification, etc.).