Keppeler 2021.

Study characteristics
Methods	Study design: randomised controlled trial Type of publication: journal publication Setting and dates: May 21 to May 23, 2021 Country: Germany Language: German
Interventions	Control letters (outlines the personal benefits of getting vaccinated against SARS‐CoV‐2) Personalised letters (contains a psychological ownership manipulation, all necessary information about the vaccine, the need to reach herd immunity, and how to schedule vaccination appointments, formatted and typeset by the municipal administration to align with the municipal corporate design, signed by the municipality’s Mayor and two public health officials)
Population	Population: general population Age: 18 and older Gender: Male, Female Ethnicity: NR Number of participants (recruited/allocated/evaluated): 27,306 Inclusion/exclusion criteria: vaccine‐eligible residents of the municipality
Outcomes	"Unique clicks," indicating the number of individuals who performed at least one click on each link (personalised link and corresponding QR code to the municipality’s information website, links to the digital scheduling software for vaccination appointments)
Notes	COI: NR Funding: NR