Sample size: planned number of observations
6,000 observations for primary outcome.
Sample for analysis: We will send 133,333 invitations each year (comprising all experimental treatments), in 2022, and 133,333 in 2023, and 133,333 in 2024.
In addition to our field experiment, the donor center will collect data on a control group of about 133,333 persons who are randomly not invited to the letter intervention, but share same characteristics as experimental subjects.
Other data collected by the donor center: Additionally, the donor center will collect data on 133,333 invitations using the letter they used prior to the intervention, only for internal monitoring.