Increasing Immunization Compliance Among Schools and Day Care Centers: Evidence from a Randomized Controlled Trial

This paper reports on the results of a randomized controlled trial in which researchers collaborated with a department of health in a mid-size city to evaluate the effectiveness of targeted communications highlighting descriptive social norms to increase immunization compliance across 700 schools. Schools were randomly selected to receive a twice-annual immunization compliance report card reporting in detail their compliance rates compared to other schools of the same school type; the comparison rates reported included the school-type average, average compliance among the top 10% of performers, and the city target of 98% compliance. Shifts in immunization compliance are tracked in a city-wide administrative vaccine registry. The results suggest that there was no significant difference in compliance rates between treatment and control schools six months post-treatment. To our knowledge, it is the first randomized controlled trial evaluating the use of descriptive social norms in increasing immunization compliance rates in a school-based setting. In addition, it serves as an example of embedding a behaviorally-informed experiment in a government program utilizing high-quality administrative data.