Targeting Behavioral Interventions Based on Baseline Motivation Increases Vaccine Uptake

The efficacy of behavioral interventions targeting policy-relevant outcomes often varies across sub-populations. Understanding and planning for heterogeneous treatment effects is critical to developing nuanced theories of human behavior and offering more useful guidance to policymakers. We identify one theory-driven source of heterogeneity in the effectiveness of behavioral interventions: individuals’ baseline motivation to adopt the encouraged activity. Through online and field experiments testing ways to encourage flu vaccination (total N=17,362), we show that an information intervention, designed to enhance interest in vaccination by correcting misconceptions, increased vaccination intentions and uptake only for those with low baseline motivation to get vaccinated. Conversely, an intervention designed to encourage follow-through by increasing the salience and convenience of vaccination only boosted vaccine uptake for those with high baseline motivation. This work highlights that aligning the mechanisms targeted by an intervention to match individuals’ baseline motivation is a theory-driven way to customize behavior change interventions.