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You’ve got mail: increasing vaccination rates

Last registered on July 20, 2023


Trial Information

General Information

You’ve got mail: increasing vaccination rates
Initial registration date
August 13, 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
August 17, 2021, 10:25 AM EDT

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

Last updated
July 20, 2023, 7:43 AM EDT

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



Primary Investigator

University of Bern

Other Primary Investigator(s)

PI Affiliation
PI Affiliation

Additional Trial Information

Start date
End date
Secondary IDs
Prior work
This trial does not extend or rely on any prior RCTs.
In light of the COVID-19 pandemic, vaccination campaigns try to further increase vaccination rates. In written reminders, we include behavioral interventions and test their influence on vaccination rates. The study comprises three distinct projects. Project 1 examines the effect of written reminders on vaccination decisions by comparing vaccination rates in our sample to an untreated comparison group. Project 2 tests the effect of social norm information included in the written reminder on the vaccination decision. Project 3 looks at the influence of a mobile vaccination team, offering on site vaccination where no appointment is needed.
External Link(s)

Registration Citation

Kulle, Anna-Corinna, Stefanie Schumacher and Frauke von Bieberstein. 2023. "You’ve got mail: increasing vaccination rates." AEA RCT Registry. July 20.
Experimental Details


Intervention Start Date
Intervention End Date

Primary Outcomes

Primary Outcomes (end points)
Vaccination rates
Primary Outcomes (explanation)

Secondary Outcomes

Secondary Outcomes (end points)
Secondary Outcomes (explanation)

Experimental Design

Experimental Design
We conduct a field experiment, sending out written reminders to get vaccinated against COVID-19 to the inhabitants of several municipalities.

Firstly, the effect of the reminder is analyzed by comparing vaccination rates to a baseline comparison group without reminder. Secondly, the impact of social norm information in the letters is compared between the treatments. Thirdly, in half of the treated municipalities, a mobile vaccination team will be on site and the influence of this offer on vaccination rates is examined.
Experimental Design Details
Randomization Method
Randomization on the household level. The treatments will be randomly assigned using a spreadsheet. In three municipalities, the information on household compositions was not available. In those cases, treatments were randomly assigned on the address-level (streetname + housenumber + postal code).

The information on the baseline vaccination rates was not known at the time of the randomization.
Randomization Unit
Household level.
Was the treatment clustered?

Experiment Characteristics

Sample size: planned number of clusters
Across the two experimental and the one control condition in the treated sample, approximately 23’500 households / unique addresses (when household information was not available), equally distributed between all three conditions. For the final sample size, vaccination rates are to be checked.
Sample size: planned number of observations
In total approximately 46’000 inhabitants receive a letter. Out of this, we expect roughly 40% to be non-vaccinated at the time of our study. This leads us to a final sample of an estimated 18’000 participants.
Sample size (or number of clusters) by treatment arms
We expect approximately 6'000 participants per treatment (in all three treatment conditions). Additionally, we expect approximately the same sample size in our basic (untreated) comparison group.
Minimum detectable effect size for main outcomes (accounting for sample design and clustering)

Institutional Review Boards (IRBs)

IRB Name
Ethics Committee University of Bern, Faculty of Business, Economics and Social Sciences
IRB Approval Date
IRB Approval Number


Post Trial Information

Study Withdrawal

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Is the intervention completed?
Intervention Completion Date
September 06, 2021, 12:00 +00:00
Data Collection Complete
Data Collection Completion Date
September 06, 2021, 12:00 +00:00
Final Sample Size: Number of Clusters (Unit of Randomization)
20 clusters (communities)
Was attrition correlated with treatment status?
Final Sample Size: Total Number of Observations
20,414 unvaccinated adults
Final Sample Size (or Number of Clusters) by Treatment Arms
10 communities per treatment arm
Data Publication

Data Publication

Is public data available?

Program Files

Program Files
Reports, Papers & Other Materials

Relevant Paper(s)

Reports & Other Materials