Information provision to mitigate discrimination of the COVID-19 vaccinators toward non-vaccinators

Last registered on March 13, 2023
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Pre-Trial

Trial Information

General Information

Title
Information provision to mitigate discrimination of the COVID-19 vaccinators toward non-vaccinators
RCT ID
AEARCTR-0011014
Initial registration date
February 28, 2023

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
March 13, 2023, 8:33 AM EDT

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

Last updated
March 13, 2023, 6:19 PM EDT

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

Locations

Country
Japan
Region

Primary Investigator

Name
Shusaku Sasaki
Affiliation
Osaka University
Contact Primary Investigator

Other Primary Investigator(s)

PI Name
Hirofumi Kurokawa
PI Affiliation
University of Hyogo
Contact Investigator

Additional Trial Information

Status
On going
Start date
2023-02-24
End date
2025-03-31
Keywords
Behavior, Crime, Violence, & Conflict, Governance, Health
Additional Keywords
COVID-19, Vaccination behavior, Vaccinated people, Unvaccinated people, Dictator game, Ingroup favoritism, Ingroup bias, Outgroup bias, Cooperation, Discrimination, Altruism, Reciprocity, Public economics, Health economics, Behavioral economics, Online laboratory experiment, Japan
JEL code(s)
Secondary IDs
Prior work
This trial does not extend or rely on any 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 conducted a follow-up experiment primarily on the above participants and examined how the ingroup favoritism, ingroup bias, and outgroup bias of vaccinated and unvaccinated participants changed during the period from January-February to December, 2022. Consequently, we found the vaccinated people’s discrimination against the unvaccinated is persistent.

The current study conducts a nationwide online experiment for the COVID019 vaccinators to discover informational interventions that can mitigate their discriminatory attitude toward non-vaccinators. The primary candidate of the intervention is information on the favorable attitude of the non-vaccinators toward the vaccinators, which we found in January-February 2022.
External Link(s)

Registration Citation

Citation
Sasaki, Shusaku and Hirofumi Kurokawa. 2023. "Information provision to mitigate discrimination of the COVID-19 vaccinators toward non-vaccinators." AEA RCT Registry. March 13. https://doi.org/10.1257/rct.11014-2.1
Sponsors & Partners
Experimental Details

Interventions

Intervention(s)
We create two treatment groups and one control group, as follows:

Treatment A: We provide information on the tendency of the COVID-19 non-vaccinators to allocate higher amounts to the vaccinators in the February 2022 experiment.

Treatment B: We provide information on the tendency of the COVID-19 non-vaccinators to allocate higher amounts to the vaccinators in the February 2022 experiment. In addition, we explain that this tendency was obvious in particular among the non-vaccinators who selected as their non-vaccination reason “I would like to get vaccinated if I could, but I cannot for health or other reasons.”

Control: We provide no additional information.
Intervention Start Date
2023-03-03
Intervention End Date
2023-03-10

Primary Outcomes

Primary Outcomes (end points)
- Ingroup favoritism
- Ingroup bias
- Outgroup bias
* Please see the analysis plan for how to create these indicators.
Primary Outcomes (explanation)

Secondary Outcomes

Secondary Outcomes (end points)
Real-world attitudes related to the COVID-19:
- Whether you do not want the COVID-19 non-vaccinators living in your neighborhood?
- Do you intend to receive the COVID-19 vaccine every year?
- Do you think priority should be given to infectious disease control, while sacrificing some socio-economic activities? Or, do you think priority should be given to socioeconomic activities, while sacrificing some infectious disease control?
- How much do you agree with the government’ decision of relaxing the rules for wearing masks?
- How much do you agree with the government’ decision of lowering the classification of the COVID-19 under the Infectious Diseases Act?
Secondary Outcomes (explanation)

Experimental Design

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

I. Anonymous: A recipient is anonymous for a vaccinated allocator.
II. Ingroup: A vaccinated allocator is informed that a recipient belongs to the ingroup. Specifically, the recipient is an individual who has received the three or more COVID-19 vaccinations up to March 2023.
III. Outgroup: A vaccinated allocator is informed that a recipient belongs to the outgroup. Specifically, the recipient is an individual who has never received the COVID-19 vaccination as of March 2023.

One vaccinated subject participates in three dictator game experiments as an allocator. We randomly set the order of the above conditions to create two groups. After we present the dictator game in the Anonymous condition (I) in both groups, we randomly present either of (II, III) or (III, II).

Furthermore, we create two treatment groups and one control group, as follows:

Treatment A: We provide information on the tendency of the COVID-19 non-vaccinators to allocate higher amounts to the vaccinators in the February 2022 experiment.

Treatment B: We provide information on the tendency of the COVID-19 non-vaccinators to allocate higher amounts to the vaccinators in the February 2022 experiment. In addition, we explain that this tendency was obvious in particular among the non-vaccinators who selected as their non-vaccination reason “I would like to get vaccinated if I could, but I cannot for health or other reasons.”

Control: We provide no additional information.

We randomly create the above two subgroups, (I, II, III) and (I, III, II), in each of the three groups Treatment A, Treatment B, and Control. Thus, the final group composition is Treatment A (I, II, III), Treatment A (I, III, II), Treatment B (I, II, III), Treatment B (I, III, II), Control (I, II, III), Control (I, III, II).

We explain more details in the attachment of the analysis plan.
Experimental Design Details
Not available
Randomization Method
Stratified randomization by a survey company. The strata are based on age and generosity in the screening survey.
Randomization Unit
Individuals.
Was the treatment clustered?
No

Experiment Characteristics

Sample size: planned number of clusters
Not clustered.
Sample size: planned number of observations
1,920 vaccinated individuals.
Sample size (or number of clusters) by treatment arms
640 vaccinated individuals are assigned to Treatment A group, 640 vaccinated individuals are assigned to Treatment B group, 640 vaccinated individuals are assigned to Control group. In each group, 320 vaccinated individuals participate in three dictator games with the order of I, II, III, while other 320 vaccinated individuals participate in three dictator games with the order of I, III, II.
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. We ensure a sample size of 320 for each subgroup in preparation for heterogeneity analyses. Reference: Balliet, D., Wu, J., & De Dreu, C. K. (2014). Ingroup favoritism in cooperation: a meta-analysis. Psychological bulletin, 140(6), 1556.
Supporting Documents and Materials
IRB

Institutional Review Boards (IRBs)

IRB Name
Center for Infectious Disease Education and Research, Osaka University IRB
IRB Approval Date
2023-01-20
IRB Approval Number
2022CRER0120-1
Analysis Plan

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