Paying people to change health behavior works in the short term but the long game is unsolved

Published in Science in One Health.

Pay someone to report a sick animal, and they probably will. Pay them per sick animal, and they might start breeding more animals to increase the odds of a payout. That tension, between the intended behavior and the unintended consequence, runs through two decades of research on financial incentives for health and environmental outcomes.

A comprehensive review published in Science in One Health synthesizes the evidence on using cash rewards and conditional payments to promote behavior change in contexts where human, animal, and environmental health intersect. The findings are encouraging in the short term and concerning in the long term.

Short-term effectiveness, long-term uncertainty

Meta-analyses consistently show that conditional financial incentives work for promoting health-related behaviors over periods of weeks to months. People respond to money. The challenge is what happens when the money stops. Evidence for sustained behavior change beyond 18 months is limited. Whether people internalize new habits or revert to baseline once incentives are withdrawn depends on factors that research has not fully untangled.

Payment for ecosystem services programs show a similar pattern: modest benefits that are highly dependent on local governance capacity, property rights security, and monitoring infrastructure. The incentive itself is rarely sufficient.

Six persistent problems

The review catalogs recurring challenges that have plagued incentive programs across domains. Additionality, proving that the incentive caused behavior that would not have happened anyway, remains difficult to establish. Monitoring compliance is straightforward for simple, observable actions like disease reporting but breaks down for complex or repeated behaviors. Collective action problems arise when the desired behavior requires group effort but incentives target individuals. Equity concerns emerge when programs disproportionately recruit influential community members or displace existing livelihoods. Moral hazard appears when payment structures accidentally reward undesirable behavior. And income effects create a particularly insidious dynamic in low-income settings: if recipients come to depend on incentive payments, they may quietly work to sustain the problem that triggers the payment.

Guinea worm: where incentives worked and where they didn't

The review uses Guinea worm eradication as a detailed case study. Designated for global eradication in 1986, when it affected approximately 3.5 million people annually across 21 countries, the disease has declined by 99.9% to just 15 human cases by 2024. Cash rewards for reporting human cases have been a successful component of this effort: reporting is individual, easily verified, and benefits the reporter directly.

But when animal infections emerged as a new obstacle, starting with dogs in Chad in 2012, the incentive design became more complicated. When rewards were paid per infected animal, some households increased dog ownership hoping to benefit from infected animals, leading to stray dog populations and disputes over reward eligibility. The program had to restructure incentives to a household basis coupled with community awareness campaigns.

Dog tethering incentives, designed to keep animals away from water sources, introduced yet another layer of complexity. Monitoring requires sustained local surveillance. Chad's program settled on approximately $5 per household per month meeting specified criteria, and empowered communities to decide how rewards were distributed, with some pooling funds for public goods.

What we still do not know

The review identifies six major knowledge gaps that persist despite two decades of research. How incentives interact with communication campaigns is poorly documented. Whether financial rewards undermine intrinsic motivation (crowding out) or enhance it (crowding in) remains inconsistently understood across contexts. Cash versus non-cash incentive effectiveness is unresolved. The precise role of conditionality, requiring behavior verification for payment, is still debated. Long-term post-incentive effects are largely unknown. And designing effective group incentives remains poorly understood.

The review's conclusion is measured: financial incentives can contribute meaningfully to health and environmental objectives, but only when carefully designed as part of comprehensive programs that include community engagement, communication, and infrastructure. When incentive programs cannot align with evidence-based design principles, alternative approaches should be pursued instead. The tool works, sometimes, for a while, under specific conditions. That is useful to know. It is also useful to know that it is not a shortcut.