Can Nudge-based Messages Encourage People with COVID-19 Vaccine Hesitancy?

Last registered on July 04, 2021

Pre-Trial

Trial Information

General Information

Title
Can Nudge-based Messages Encourage People with COVID-19 Vaccine Hesitancy?
RCT ID
AEARCTR-0007892
Initial registration date
June 28, 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
June 29, 2021, 2:23 PM EDT

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

Last updated
July 04, 2021, 5:21 AM EDT

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

Locations

Region

Primary Investigator

Affiliation
Tohoku Gakuin University

Other Primary Investigator(s)

PI Affiliation
Osaka University
PI Affiliation
National Institute of Infectious Diseases

Additional Trial Information

Status
On going
Start date
2021-07-02
End date
2022-07-31
Secondary IDs
Abstract
Some studies showed that young people have lower intentions of COVID-19 vaccination than older people. Our previous study found that nudge-based messages providing information on others’ decisions and behaviors could strengthen the vaccination intentions of the older people, but do not have the same effects for the young people (Sasaki, Saito, and Ohtake, 2021). Therefore, as of June 30, 2021, we have not yet found an effective message to encourage the vaccination of the Japanese people other than the older people.

This study again explores nudge-based messages that can encourage COVID-19 vaccination of youth and middle-aged people with low vaccination intentions at baseline. Our preliminary analysis indicates the possibility that the high need for going out and a rise in altruism among younger people may close the gap in vaccination intentions between older and younger people. One foreign study reported that the message, “Full shot reserved for you,” has a large effect in promoting people to receive the seasonal flu vaccine (Milkman et al., 2021). The similar message may be effective for promoting COVID-19 vaccination of people in Japan. Taking the pre-analysis and the foreign study into account, we develop nudge-based messages for the vaccination of youth and middle-aged people in Japan.

We conduct an online survey experiment toward 3,000 respondents of youth and middle-aged people (25-49 years old) residing throughout Japan. In the experiment, we randomly divide the respondents into five groups. We set a hypothetical question to capture their willingness-to pay (WTP) for COVID-19 vaccine, while displaying messages by group. The five groups consist of one control group and four treatment groups, which display nudge-based messages. After the WTP question, we set questions to capture the degrees of respondents’ autonomous decision-making and emotional burden, because it is important from a policy perspective to find out a nudge-based message that can strengthen people’s vaccination intention and at the same time consider their autonomous decision-making and emotional burden. We set another question to capture respondents’ opinions on whether other people should receive the vaccine.

We use the experimental data and estimate the effects of the four nudge-based messages on the respondents’ WTP, autonomy, emotional burden, and opinion on others’ vaccination. We also investigate whether the messages’ effects are heterogeneous by age, gender, and prior vaccination intention.

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. We examine for each group how many respondents changed their choice.

References:
- Sasaki, S., Saito, T., and Ohtake, F. 2021. Nudges for COVID-19 voluntary vaccination: How to explain peer information? Osaka University Discussion Papers In Economics And Business, No.2107.
- Milkman, K.L. et al. 2021. A Mega-Study of Text-Based Nudges Encouraging Patients to Get Vaccinated at an Upcoming Doctor’s Appointment. Proceedings of the National Academy of Sciences, 118(20), e2101165118.
External Link(s)

Registration Citation

Citation
Sasaki, Shusaku, Fumio Ohtake and Tomoya Saito. 2021. "Can Nudge-based Messages Encourage People with COVID-19 Vaccine Hesitancy?." AEA RCT Registry. July 04. https://doi.org/10.1257/rct.7892
Experimental Details

Interventions

Intervention(s)
We randomly assign survey respondents to either of one control group and four treatment groups with nudge-based messages.
Intervention Start Date
2021-07-02
Intervention End Date
2021-07-06

Primary Outcomes

Primary Outcomes (end points)
Willingness to pay for COVID-19 vaccine
Primary Outcomes (explanation)
The respondents are first asked: “Suppose you can receive this vaccine without having to pay out-of-pocket, will you visit the vaccination camp and receive it?” Next, those who answer they will receive the free vaccine proceed to the question on the payment setting, while those who answer that they will not, proceed to the question on the receipt setting. The questions have a Multiple Price List format, and we define WTP as the midpoint of the amounts around the switching point.

Secondary Outcomes

Secondary Outcomes (end points)
1) Indicators of respondents’ autonomous decision-making and emotional burden
2) An indicator of respondents’ opinions on other people’s vaccination
Secondary Outcomes (explanation)
1) “Did you want to receive the vaccine voluntarily?” (voluntary), “Did you think you were being forced to receive the vaccine?” (forced), “Did you feel distressed when you received the explanation of the vaccine?” (distressed), and “Did you feel that the explanation of the vaccine needed to be improved?” (should be improved). The questions are rated on a five-point scale.
2) “Do you think that other people should receive COVID-19 vaccine?” The question is rated on a five-point scale.

Experimental Design

Experimental Design
In July 2021, we conduct an online survey experiment with the following details. We recruit totally 3,000 survey respondents of youth and middle-aged people (25-49 years old) residing throughout Japan from response monitors of a survey company. We randomly divide survey respondents into five groups. In the survey, we set a hypothetical question to capture the respondents’ willingness-to pay (WTP) for COVID-19 vaccine, while displaying messages by group. The control group provides an objective explanation of the vaccine. In addition to the explanation, the four treatment groups display nudge-based messages. Before and after the WTP question, we set questions to capture the respondents’ socio-economic attributes, prior vaccination intention, psychological and behavioral economic characteristics, health status, infection prevention attitudes and behaviors, indicators of autonomous decision making and emotional burden, an indicator of respondents’ opinions on other people’s vaccination, 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.
Experimental Design Details
In July 2021, we conduct an online survey experiment with the following details. We recruit totally 3,000 survey respondents of youth and middle-aged people (25-49 years old) residing throughout Japan from response monitors of a survey company. We randomly divide survey respondents into five groups. In the survey, we set a hypothetical question to capture the respondents’ willingness-to pay (WTP) for COVID-19 vaccine, while displaying messages by group. The control group provides an objective explanation of the vaccine. In addition to the explanation, the four treatment groups display the following nudge-based messages, respectively: “Vaccination will protect you and your dear ones from COVID-19” (for the treatment group A), “Vaccination enables you to visit your dear ones with peace of mind” (for the treatment group B), “Vaccination reduces the likelihood that you will infect people close to you without realizing it” (for the treatment group C), and “A vaccine is reserved for you” (for the treatment group D). Before and after the WTP question, we set questions to capture the respondents’ socio-economic attributes, prior vaccination intention, psychological and behavioral economic characteristics, health status, infection prevention attitudes and behaviors, indicators of autonomous decision making and emotional burden, an indicator of respondents’ opinions on other people’s vaccination, 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, gender, and area of residence.
Randomization Unit
Individuals.
Was the treatment clustered?
No

Experiment Characteristics

Sample size: planned number of clusters
N/A
Sample size: planned number of observations
3,000 individuals (The number may vary. Even in that case, the number and composition of each group will be equal.)
Sample size (or number of clusters) by treatment arms
600 individuals in the control group, 600 individuals in the treatment group A, 600 individuals in the treatment group B, 600 individuals in the treatment group C, and 600 individuals in the treatment group D.
Minimum detectable effect size for main outcomes (accounting for sample design and clustering)
IRB

Institutional Review Boards (IRBs)

IRB Name
Graduate School of Economics, Osaka University IRB
IRB Approval Date
2021-06-16
IRB Approval Number
N/A

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