How to explain peer information: Nudging people to have a stronger intention to receive the COVID-19 vaccine

Last registered on January 16, 2022
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Pre-Trial

Trial Information

General Information

Title
How to explain peer information: Nudging people to have a stronger intention to receive the COVID-19 vaccine
RCT ID
AEARCTR-0007361
Initial registration date
March 14, 2021

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 15, 2021, 10:55 AM EDT

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

Last updated
January 16, 2022, 11:00 PM EST

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
Tomoya Saito
PI Affiliation
National Institute of Infectious Diseases
PI Name
Fumio Ohtake
PI Affiliation
Osaka University

Additional Trial Information

Status
Completed
Start date
2021-03-16
End date
2021-12-31
Keywords
Behavior, Health
Additional Keywords
COVID-19, Willingness to Pay, WTP, Vaccination Behavior, Nudge, Social Information, Peer Effect, Sludge, Autonomy, Health Economics, Behavioral Economics, Survey Experiment, Japan
JEL code(s)
Secondary IDs
Prior work
This trial does not extend or rely on any prior RCTs.
Abstract
We study how to explain peer information to encourage people to have a strong intention to receive the COVID-19 vaccine. Prior research has shown that introducing that many people have the intention to receive the vaccine can strengthen the vaccination intention of other people. However, if such the introduction inhibits their autonomous decision-making, it may be a sludge rather than a nudge. Thus, it is important from a policy perspective to clarify the way to explain peer information that can strengthen people’s vaccination intention but at the same time does not inhibit their autonomous decision-making.

We conduct an online survey experiment toward 1,600 respondents of young people (25-34 years old) and elderly people (65-74 years old) residing throughout Japan. We randomly divide the survey respondents into four groups. We set in the survey a hypothetical question to capture their willingness-to pay (WTP) for the COVID-19 vaccine, while displaying messages by group. The four groups consist of three treatment groups, which explain the peer information in different ways, and one control group. After the hypothetical question, we set questions to capture the degrees of autonomous decision-making. We use the experimental data and estimate the effects of the three treatments on the WTP and the autonomous degrees. We also investigate whether the effects are heterogeneous by socio-economic attributes, psychological and behavioral economic characteristics, health status, infection prevention attitudes and behaviors, etc.

At the end of the survey, we explain to the respondents that we have conducted a randomized controlled trial in the survey and its contents and purpose. We then ask them if they would like to change their choice regarding whether or not to receive the vaccine. We examine for each group how many respondents changed their choice.
External Link(s)

Registration Citation

Citation
Sasaki, Shusaku, Fumio Ohtake and Tomoya Saito. 2022. "How to explain peer information: Nudging people to have a stronger intention to receive the COVID-19 vaccine." AEA RCT Registry. January 16. https://doi.org/10.1257/rct.7361-1.4000000000000004
Sponsors & Partners
Experimental Details

Interventions

Intervention(s)
Intervention Start Date
2021-03-16
Intervention End Date
2021-03-19

Primary Outcomes

Primary Outcomes (end points)
Willingness to pay for the COVID-19 vaccine
Primary Outcomes (explanation)

Secondary Outcomes

Secondary Outcomes (end points)
Indicators of autonomous decision making (5-point scale responses for the questions of “did you want to receive the vaccine voluntarily?”, “did you think you were being forced to receive the vaccine?”, “did you feel distressed when you received the explanation of the vaccine?”, and “did you feel that the explanation of the vaccine needed to be improved?”)
Secondary Outcomes (explanation)

Experimental Design

Experimental Design
We randomly assign survey respondents to either of one control group and three treatment groups. The treatment group A provides a message explaining the proportion of people who have an intention to receive the vaccine. The treatment group B provides messages explaining that the more people who receive the vaccine, the more people who have an intention to do so, and that people’s vaccination behavior can encourage the vaccination behavior of those around them. The treatment group C provides messages emphasizing the similar contents of the treatment group B by loss-framing.
Experimental Design Details
In March 2021, we conduct an online survey experiment with the following details. We recruit totally 1,600 survey respondents of young people (25-34 years old) and elderly people (65-74 years old) residing throughout Japan from the response monitors of a survey company. We randomly divide the survey respondents into four groups. In the survey, we set a hypothetical question to capture the respondents’ willingness-to pay (WTP) for the COVID-19 vaccine, while displaying messages by group. The control group provides an objective explanation of the vaccine. In addition to the explanation, the three treatment groups display the following nudge-based messages, respectively: “6 to 7 out of 10 people in your age group answered that they would receive this vaccine” (for the young respondents in the treatment group A), “7 to 8 out of 10 people in your age group answered that they would receive this vaccine” (for the elderly respondents in the treatment group A), “The more people who receive this vaccine, the more people who have an intention to do so. Your vaccination behavior can encourage the vaccination behavior of the people around you” (for the treatment group B), and “The more people who receive this vaccine, the more people who have an intention to do so. If you do not receive the vaccine, the people around you also may not do so.” Before and after the hypothetical question, we set questions to capture the respondents’ socio-economic attributes, psychological and behavioral economic characteristics, health status, infection prevention attitudes and behaviors, indicators of autonomous decision making, and attitudes toward the vaccine. At the end of the survey, we explain to the respondents that we have conducted a randomized controlled trial in the survey and its content and purpose. We then ask them if they would like to change their choice regarding whether or not to receive the vaccine.
Randomization Method
Stratified randomization by a survey company. The strata are based on age and gender.
Randomization Unit
Individual
Was the treatment clustered?
No

Experiment Characteristics

Sample size: planned number of clusters
N/A
Sample size: planned number of observations
1,600 individuals
Sample size (or number of clusters) by treatment arms
400 individuals in the control group, 400 individuals in the treatment group A, 400 individuals in the treatment group B, and 400 individuals in the treatment group C
Minimum detectable effect size for main outcomes (accounting for sample design and clustering)
Supporting Documents and Materials
IRB

Institutional Review Boards (IRBs)

IRB Name
Graduate School of Economics, Osaka University IRB
IRB Approval Date
2021-02-16
IRB Approval Number
N/A
Analysis Plan

Post-Trial

Post Trial Information

Study Withdrawal

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Intervention

Is the intervention completed?
Yes
Intervention Completion Date
March 18, 2021, 12:00 +00:00
Data Collection Complete
Yes
Data Collection Completion Date
March 18, 2021, 12:00 +00:00
Final Sample Size: Number of Clusters (Unit of Randomization)
Was attrition correlated with treatment status?
No
Final Sample Size: Total Number of Observations
1,595 individuals
Final Sample Size (or Number of Clusters) by Treatment Arms
399 individuals in control, 399 individuals in comparison group, 399 individuals in influence-gain group, and 398 individuals in influence-loss group
Data Publication

Data Publication

Is public data available?
Yes
Public Data URL
https://doi.org/10.1016/j.socscimed.2021.114561

Program Files

Program Files
Yes
Program Files URL
https://doi.org/10.1016/j.socscimed.2021.114561
Reports, Papers & Other Materials

Relevant Paper(s)

Abstract
Vaccination promotion is a crucial strategy to end the COVID-19 pandemic; however, individual autonomy should also be respected. This study aimed to discover other-regarding information nudges that can reinforce people's intention to receive the COVID-19 vaccine without impeding their autonomous decision-making. In March 2021, we conducted an online experiment with 1595 people living throughout Japan, and randomly assigned them either of one control group and three treatment groups that received messages differently describing peer information: control, comparison, influence-gain, and influence-loss. We compared each message's effects on vaccination intention, autonomous decision-making, and emotional response. We found that the influence-gain nudge was effective in increasing the number of older adults who newly decided to receive the vaccine. The comparison and influence-loss nudges further reinforced the intention of older adults who had already planned to receive it. However, the influence-loss nudge, which conveys similar information to the influence-gain nudge but with loss-framing, increased viewers' negative emotion. These messages had no promoting effect for young adults with lower vaccination intentions at baseline. Based on the findings, we propose governments should use different messages depending on their purposes and targets, such as comparison instead of influence-loss, to encourage voluntary vaccination behavior.
Citation
Sasaki, S., Saito, T., and Ohtake, F. (2022). Nudges for COVID-19 voluntary vaccination: How to explain peer information? Social Science & Medicine 292, No.114561.
URL
https://doi.org/10.1016/j.socscimed.2021.114561

Reports & Other Materials