Using Implementation Intentions Prompts to Enhance Influenza Vaccination Rates.

Milkman et al. (2011)
Katy Milkman,David Laibson,James Choi,Brigitte Madrian,John Beshears
Summary by 
Mark Egan

A field experiment prompted people to form implementation intentions about influenza vaccination. Those who received the prompt to write down just a date had a vaccination rate 1.5 percentage points higher than the control group, which was statistically insignificant. Those who received the more specific prompt to write down both a date and a time had a 4.2 percentage point higher vaccination rate, a difference that is both statistically significant and of meaningful magnitude.

A randomized evaluation found that writing both a date and time increased the number of employees getting their flu shots.. Employees who received the more detailed "time plan" mailer were 4 percentage points more likely than those who received the standard mailer to get their shot (37.1% compared to 33.1%).