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Field
Abstract
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Before
This study will reveal how sending nudge-based messages to correct the false belief “I have rubella antibodies” 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 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 men 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 approcimately 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 found 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 was actually infected with chickenpox or measles, nor rubella).” We focused 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 Kanagawa, 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 yes been tested for rubella antibodies during FY2019 to FY2021 (N=22,526). We stratify the subjects by 13 residential regions and randomly assign them to three groups, including a control group and two treatment groups. The control group will receive coupons and a leaflet developed by the local government, while the two treatment groups will additionally receive nudge-based messages developed by us in two ways.
We will receive anonymized 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.
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After
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 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 approcimately 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 was 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 Kanagawa, 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 yes been tested for rubella antibodies during FY2019 to FY2021 (N=22,526). We stratify the subjects by 13 residential regions and randomly assign them to three groups, including a control group and two treatment groups. The control group will receive coupons and a leaflet developed by the local government, while the two treatment groups will additionally receive nudge-based messages developed by us in two 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.
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Field
Experimental Design (Public)
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Before
In addition to a control group, we use the two interventions to create two treatment groups. Nudge A group will receive only one intervention, “enclosing a nudge-based flyer.” The Nudge B group will receive two interventions, “printing a nudge-based message on envelop” and “enclosing a nudge-based flyer.” All the three groups receive the groups 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 interventions.
Before starting the experiment, we receive from the local government a list of the target population for MHLW’s FY2022 measures against rubella in order to conduct random assignment. The data contains information on individual ID, age, and region of residence. The target population for MHLW’s FY2022 measures against rubella is not only (a) those who have not received either antibody testing or vaccination, but also (b) those who have received antibody testing and have not been vaccinated despite negative results. The data can identify the type of subjects.
We employ a stratified randomization method by 13 regions. To begin with, we restrict the experiment to those categorized as the type (a). However, those categorized as the type (b) will receive the same mailings as the control group. Our analysis excludes this group, and we call this group the Exclusion group. We then stratify the subjects according to the 13 regions and randomly assign them to the three groups per region. The allocation ratio is equal among regions. See the Analysis plan for details.
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After
In addition to a control group, we use the two interventions to create two treatment groups, including Nudge A and Nudge B. Nudge A group will receive only one intervention, “enclosing a nudge-based flyer.” The Nudge B group will receive two interventions, “printing a nudge-based message on envelop” and “enclosing a nudge-based flyer.”
All the three groups will receive the groups and other explanatory materials, including a list of medical institutions that offer the testing and vaccination, while only the control group will receive no nudge-based intervention.
Before starting the experiment, we receive from the local government a list of the target population for MHLW’s FY2022 measures against rubella in order to conduct random assignment. The data contains information on individual ID, age, and region of residence. The target population for MHLW’s FY2022 measures against rubella is not only (a) those who have not received either antibody testing or vaccination, but also (b) those who have received antibody testing and have not been vaccinated despite negative results. The data can identify the type of subjects.
We employ a stratified randomization method by 13 regions. To begin with, we restrict the experiment to those categorized as the type (a). However, those categorized as the type (b) will receive the same mailings as the control group. Our analysis excludes this group, and we call this group the Exclusion group. We then stratify the subjects according to the 13 regions and randomly assign them to the three groups per region. The allocation ratio is equal among regions. See the Analysis plan for details.
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Field
Intervention (Hidden)
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Before
We specifically describe two interventions. (1) enclosing a nudge-based flyer explaining how and why their belief could be false and the social influences of rubella vaccination, and (2) printing on the envelop a nudge-based message which emphasizes the possibility that people’s belief that they have antibodies for rubella may false.
Both of the interventions use message, “Don’t you believe that you have antibodies for rubella?”
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After
We specifically describe two interventions. (1) enclosing a nudge-based flyer explaining how and why people’s belief that they have antibodies for rubella could be false and the social influences of rubella vaccination, and (2) printing on the envelop a nudge-based message which emphasizes the possibility that their belief may be false.
Both of the interventions use message, “Don’t you believe that you have antibodies for rubella?”
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