Banerjee and Duflo's vaccination study found that a reliable, predictable schedule alone nearly tripled immunization rates, and adding a small incentive (worth about $0.75) increased them sixfold. The finding challenged the assumption that low immunization rates in rural India reflected vaccine hesitancy — most parents wanted to vaccinate but faced coordination problems (not knowing when camps would be held) and procrastination. The lentil incentive addressed both by giving parents an immediate benefit and a concrete date to plan around. The result is one of the most cited demonstrations of how behavioral frictions, not preferences, drive low take-up of beneficial programs.
Research question
"Do reminders and small incentives increase childhood immunization rates in rural India?"
Methodology
Intervention
Three arms: reliable immunization camp schedule (information only), reliable schedule plus small incentive (1 kg lentils per immunization), control (status quo)