A Dictator Game Experiment with the COVID-19 Vaccinated and Unvaccinated People: A Follow-up

Last registered on June 20, 2023

Pre-Trial

Trial Information

General Information

Title
A Dictator Game Experiment with the COVID-19 Vaccinated and Unvaccinated People: A Follow-up
RCT ID
AEARCTR-0010611
Initial registration date
December 09, 2022

Initial registration date is when the trial was registered.

It corresponds to when the registration was submitted to the Registry to be reviewed for publication.

First published
December 13, 2022, 11:21 PM EST

First published corresponds to when the trial was first made public on the Registry after being reviewed.

Last updated
June 20, 2023, 1:47 AM EDT

Last updated is the most recent time when changes to the trial's registration were published.

Locations

Region

Primary Investigator

Affiliation
The University of Osaka

Other Primary Investigator(s)

PI Affiliation
University of Hyogo

Additional Trial Information

Status
On going
Start date
2022-12-02
End date
2025-03-31
Secondary IDs
Prior work
This trial is based on or builds upon one or more prior RCTs.
Abstract
In January-February 2022, we conducted financially incentivized dictator games with those with two COVID-19 vaccinations and those with zero vaccination in Japan (N=1,578), and ascertained their favorable or hostile attitudes toward each other, by using ingroup favoritism. We measured ingroup favoritism as the difference in the allocated amounts between to ingroup members with the same vaccination status and to outgroup members with a different status. Our analyses suggested that the vaccinated people behaved more discriminately toward outgroup members, compared to the unvaccinated people. The vaccinated people showed strong ingroup favoritism, which were shaped mainly by their outgroup bias of decreasing the money amount allocated to an unvaccinated pair, their outgroup member. In contrast, the unvaccinated people did not exhibit such the ingroup favoritism, on average. Their outgroup bias was found in the rather opposite direction of the hypothesis, and they tended to increase the amount to a vaccinated pair, their outgroup member. We found this tendency in particular from the unvaccinated who selected as their non-vaccination reason “I would like to get vaccinated if I could, but I cannot for health or other reasons.” Furthermore, we confirmed significant associations between their ingroup favoritism and attitudes regarding the COVID-19 policies, suggesting that the biases would have some degree of social influence in the real world.

In December 2022, we will conduct a follow-up experiment primarily on the above participants and examine how the ingroup favoritism, ingroup bias, and outgroup bias of vaccinated and unvaccinated participants change during the period from January-February to December, 2022. We will investigate whether the vaccinated people’s discrimination against the unvaccinated is temporary or persistent, from which we will derive policy implications.
External Link(s)

Registration Citation

Citation
Sasaki, Shusaku and Hirofumi Kurokawa. 2023. "A Dictator Game Experiment with the COVID-19 Vaccinated and Unvaccinated People: A Follow-up." AEA RCT Registry. June 20. https://doi.org/10.1257/rct.10611-1.2
Experimental Details

Interventions

Intervention(s)
We conduct dictator game experiments in the following five conditions:

I. Anonymous: A recipient is anonymous for an allocator. The allocator is also anonymous for the recipient.

II. Current-Ingroup: An allocator is informed that a recipient belongs to the current-ingroup (for the vaccinated sample, the recipient is an individual who has received the three or more COVID-19 vaccinations up to December 2022; for the unvaccinated sample, he/she is an individual who has never received the COVID-19 vaccination as of December 2022). The allocator is anonymous for the recipient.

III. Current-Outgroup: An allocator is informed that a recipient belongs to the current-outgroup (for the vaccinated sample, the recipient is an individual who has never received the COVID-19 vaccination as of December 2022; for the unvaccinated sample, he/she is an individual who has received the three or more COVID-19 vaccinations up to December 2022). The allocator is anonymous for the recipient.

IV. Previous-Ingroup: An allocator is informed that a recipient belongs to the previous-ingroup (for the vaccinated sample, the recipient is an individual who received the two COVID-19 vaccinations as of January-February 2022; for the unvaccinated sample, he/she is an individual who did not receive any COVID-19 vaccination as of January-February 2022). The allocator is anonymous for the recipient.

V. Previous-Outgroup: An allocator is informed that a recipient belongs to the previous-outgroup (for the vaccinated sample, the recipient is an individual who did not receive any COVID-19 vaccination as of January-February 2022; for the unvaccinated sample, he/she is an individual who received the two COVID-19 vaccinations as of January-February 2022). The allocator is anonymous for the recipient.
Intervention (Hidden)
Intervention Start Date
2022-12-15
Intervention End Date
2022-12-20

Primary Outcomes

Primary Outcomes (end points)
Allocation in the dictator game experiment (more specifically, within-difference between the allocated amounts in the second dictator game and the first anonymous dictator game; Details for the analysis plan)
Primary Outcomes (explanation)

Secondary Outcomes

Secondary Outcomes (end points)
Attitudes toward the COVID-19-related policies (Balancing infectious disease control and socio-economic activities, vaccination certification, etc.)
Secondary Outcomes (explanation)

Experimental Design

Experimental Design
We conduct dictator game experiments in the following five conditions:

I. Anonymous: A recipient is anonymous for an allocator. The allocator is also anonymous for the recipient.

II. Current-Ingroup: An allocator is informed that a recipient belongs to the current-ingroup (for the vaccinated sample, the recipient is an individual who has received the three or more COVID-19 vaccinations up to December 2022; for the unvaccinated sample, he/she is an individual who has never received the COVID-19 vaccination as of December 2022). The allocator is anonymous for the recipient.

III. Current-Outgroup: An allocator is informed that a recipient belongs to the current-outgroup (for the vaccinated sample, the recipient is an individual who has never received the COVID-19 vaccination as of December 2022; for the unvaccinated sample, he/she is an individual who has received the three or more COVID-19 vaccinations up to December 2022). The allocator is anonymous for the recipient.

IV. Previous-Ingroup: An allocator is informed that a recipient belongs to the previous-ingroup (for the vaccinated sample, the recipient is an individual who received the two COVID-19 vaccinations as of January-February 2022; for the unvaccinated sample, he/she is an individual who did not receive any COVID-19 vaccination as of January-February 2022). The allocator is anonymous for the recipient.

V. Previous-Outgroup: An allocator is informed that a recipient belongs to the previous-outgroup (for the vaccinated sample, the recipient is an individual who did not receive any COVID-19 vaccination as of January-February 2022; for the unvaccinated sample, he/she is an individual who received the two COVID-19 vaccinations as of January-February 2022). The allocator is anonymous for the recipient.

One subject participates in five dictator game experiments as an allocator. We randomly set the order of the above conditions to create four groups in the vaccinated and unvaccinated samples, respectively. After we present the dictator game in the Anonymous condition (I) in all the four groups, we randomly present either of (II, III) or (III, II). We then randomly present either of (IV, V) or (V, IV). Consequently, each of the vaccinated and unvaccinated samples have four groups.

Furthermore, to address potential order effects caused by successive participation in the dictator games, we create a control group where we present the anonymous dictator game (I) five times. Totally, each of the vaccinated and unvaccinated samples have five groups, including the control group.

We explain more details in the attachment of the analysis plan.
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.).
Randomization Method
We conduct stratified randomization respectively for existing participants and added ones. The strata are based on the previous experiment’s group assignment for the existing participants, and the strata are based on age and generosity for the added participants.
Randomization Unit
Individuals.
Was the treatment clustered?
No

Experiment Characteristics

Sample size: planned number of clusters
N/A
Sample size: planned number of observations
1,600 individuals. 800 “vaccinated individuals” who received the two COVID-19 vaccinations as of January-February 2022, and 800 “unvaccinated individuals” who did not receive the COVID-19 vaccination as of January-February 2022.
Sample size (or number of clusters) by treatment arms
800 vaccinated individuals include four treatment groups (4*160 vaccinated individuals=640 vaccinated individuals) and one control group (160 vaccinated individuals). Similarly, 800 unvaccinated individuals include four treatment groups (4*160 unvaccinated individuals=640 unvaccinated individuals) and one control group (160 unvaccinated individuals).
Minimum detectable effect size for main outcomes (accounting for sample design and clustering)
In the meta-analysis (Balliet et al., 2014), d of the ingroup-favoritism is 0.32. When we calculate the necessary sample size under the conditions of power=0.8 and alpha=0.05, it becomes 155 for each group. Reference: Balliet, D., Wu, J., & De Dreu, C. K. (2014). Ingroup favoritism in cooperation: a meta-analysis. Psychological bulletin, 140(6), 1556.
IRB

Institutional Review Boards (IRBs)

IRB Name
Center for Infectious Disease Education and Research, Osaka University IRB
IRB Approval Date
2022-11-15
IRB Approval Number
2022CRER1115-2
Analysis Plan

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Post-Trial

Post Trial Information

Study Withdrawal

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Intervention

Is the intervention completed?
No
Data Collection Complete
Data Publication

Data Publication

Is public data available?
No

Program Files

Program Files
Reports, Papers & Other Materials

Relevant Paper(s)

Reports & Other Materials