Applying Behavioral Insights to Rubella Antibody Testing and Vaccination: A Field Experiment in Ibaraki, Japan

Last registered on June 16, 2022

Pre-Trial

Trial Information

General Information

Title
Applying Behavioral Insights to Rubella Antibody Testing and Vaccination: A Field Experiment in Ibaraki, Japan
RCT ID
AEARCTR-0009453
Initial registration date
June 13, 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
June 15, 2022, 10:17 AM EDT

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

Last updated
June 16, 2022, 1:34 AM EDT

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

Locations

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Primary Investigator

Affiliation
Graduate School of Economics, Osaka University

Other Primary Investigator(s)

PI Affiliation
Center for Infectious Disease Education and Research, Osaka University
PI Affiliation
Center for Infectious Disease Education and Research, Osaka University

Additional Trial Information

Status
On going
Start date
2022-06-15
End date
2025-03-31
Secondary IDs
Prior work
This trial does not extend or rely on any prior RCTs.
Abstract
This study will reveal how sending nudge-based messages to correct the false belief “I have antibodies for rubella” affects the uptake of rubella antibody testing and vaccination.

In Japan, herd immunity to rubella can be obtained by achieving a 90% antibody prevalence rate for rubella in all generations. While the rate has reached over 90% among most generations, the rate for males born between 1962 and 1978 is approximately 80%, because they were previously excluded from the routine vaccinations and have had few natural infections. Therefore, the Ministry of Health, Labor, and Welfare (MHLW) has set a policy goal of increasing the antibody prevalence rate of this generation of males from 80% to 90% to obtain herd immunity against rubella.

To achieve this goal, free coupons for rubella antibody testing and vaccination have been mailed to males of the target generation from FY2019 to FY2021 by local governments. The MHLW expected that the policy goal described above could have been achieved if approximately 1.9 million had used these coupons and received the rubella vaccination. However, as of October 2021, the number of people vaccinated remained low at about 740,000 (about 39% of the target number). Therefore, the MHLW decides to re-distribute free coupons starting also in FY2022. The coupons will be mailed to males born between 1962 and 1978 who have not received an antibody testing during FY2019 to FY2021, or who have not been vaccinated even though they are eligible for the vaccination.

Taking the results of our preliminary survey into account, we find that the subjects could form false beliefs, such as “I received the rubella vaccine when I was a child" (even though there were no routine rubella vaccinations for their generations) or “I was infected with rubella in the past" (even though they were actually infected with chickenpox or measles, not rubella). We focus on the possibility that these misperceptions may be a bottleneck of preventing them from getting tested and vaccinated. In this study, we will develop a nudge-based message to correct this belief and conduct a field experiment in cooperation with a local government in Ibaraki, Japan, to evaluate the effect of the message.

The subjects of our field experiment are males born between 1962 and 1978 who reside in that local government’s area and who have not yet been tested for rubella antibodies during FY2019 to FY2021 (N = 5,568). We employ cluster randomization at the regional level for the allocation of four experimental arms. The control group will receive coupons and a leaflet developed by the local government, while the three treatment groups will additionally receive nudge-based messages developed by us in three different ways.

We will receive anonymized administrative data from the local government on the date of the antibody test, the result of the antibody test, and the date of vaccination. Our primary outcomes are “antibody testing behavior” and “vaccination behavior”. Using these binary variables, we estimate the average effect of nudge-based interventions on vaccination, e.g., through linear probability models. Our secondary outcomes are “date of antibody test” and “vaccination date,” in addition to “whether the antibody test result was negative.” Using these date variables, we estimate the effect of the interventions on the vaccination date using, for example, a survival analysis.
External Link(s)

Registration Citation

Citation
Kato, Hiroki, Fumio Ohtake and Shusaku Sasaki. 2022. "Applying Behavioral Insights to Rubella Antibody Testing and Vaccination: A Field Experiment in Ibaraki, Japan." AEA RCT Registry. June 16. https://doi.org/10.1257/rct.9453
Experimental Details

Interventions

Intervention(s)
In Japan, local governments mail to males in the targeted generation “coupons,” by which they can receive free antibody testing and vaccination against rubella. In general, the local governments send the coupons and other explanatory materials, including a list of medical institutions that offer the testing and vaccination.

In a collaboration with a local government in Ibaraki, Japan, we add the following two interventions to mailings: (1) enclosing a nudge-based flyer into the envelope; (2) printing a nudge-based message on the envelope.
Intervention Start Date
2022-06-15
Intervention End Date
2023-03-31

Primary Outcomes

Primary Outcomes (end points)
(1) Whether or not you received the rubella antibody testing (binary)
(2) Whether or not you have received the rubella vaccination (binary)
Primary Outcomes (explanation)

Secondary Outcomes

Secondary Outcomes (end points)
(1) Binary variable of whether the antibody test result is negative (i.e., whether vaccination is required)
(2) When you received the rubella antibody testing (date)
(3) When you received the rubella vaccination (date)
Secondary Outcomes (explanation)

Experimental Design

Experimental Design
In addition to a control group, we use two interventions to create three treatment groups, including Nudge A, Nudge B, and Nudge C. Nudge A group will receive only one nudge-based intervention, “enclosing a nudge-based flyer.” The Nudge B group will receive only another nudge-based intervention, “printing a nudge-based message on envelope.” The Nudge C group will receive both of the two interventions, “enclosing a nudge-based flyer” and “printing a nudge-based message on envelope.”

All the four groups will receive the coupons and other explanatory materials, including a list of medical institutions that offer the testing and vaccination, while only the control group receive no nudge-based intervention.

The local government assigns subjects to one of the four experimental arms as randomly as possible by its reasonable administrative procedures. First, they pick up two regions with similar attributes from totally eight geographical regions. Then, they randomly assign one region to the intervention of enclosing a nudge-based flyer.

Next, they divide the sample in each region into two groups, based on whether or not subjects have received free coupon for rubella antibody testing and vaccination until FY2021. Within each region and each group, they sort subjects by zip code, street address, and individual ID, and assign them in the first half of the group to the intervention of printing a nudge-based message on envelope. See the Analysis plan for details.
Experimental Design Details
Not available
Randomization Method
Cluster randomization by the local government. See the section of Experimental Design in detail.
Randomization Unit
Region.
Was the treatment clustered?
Yes

Experiment Characteristics

Sample size: planned number of clusters
2 regions
Sample size: planned number of observations
5,568 individuals
Sample size (or number of clusters) by treatment arms
1,098 individuals (1 cluster) in the control; 1,685 individuals (1 cluster) in the nudge A; 1,099 individuals (1 cluster) in the nudge B; 1,686 individuals (1 cluster) in the nudge C.
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
2022-04-27
IRB Approval Number
R40427
IRB Name
Center for Infectious Disease Education and Research, Osaka University IRB
IRB Approval Date
2022-04-28
IRB Approval Number
2022CRER0428
Analysis Plan

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