Birthdate-Based Randomization Design
Field experiments in public administration often face ethical and logistically complex barriers when assigning individuals randomly to social policies.
Picture this
Assigning people based on their birthdate works like splitting a crowd into two equal groups based on whether their ticket number is odd or even. Because birthdays are evenly distributed across the population, everyone born in the first half of the month gets one treatment and those born in the second half get another, creating two balanced groups without bias.
What the evidence says
Produced balanced baseline demographic distributions across treatment and control groups while enabling evaluation of policy regime shifts.
- Who
- N = 5,180 total inflow individuals (human, Denmark: Storstrøm and Southern Jutland counties).
- How
- Randomized Controlled Trial assigning individuals born on days 1–15 to treatment and days 16–31 to control.
What to do
Assign social trial participants using birthdate splits (1st–15th vs. 16th–31st) to implement transparent, unmanipulable field randomization.
From the source
"specifically, all individuals in the two counties who became unemployed during this period were randomized into a treatment and a control group based on their birthday; those born on the 1st to the 15th were given the treatment, and those born on the 16th to the 31st were not."
Experimental Evidence on the Nature of the Danish Employment Miracle