New review calls for better integration of scale in obesity prevention cost-effectiveness studies
A new systematic scoping review published in Obesity Reviews examines how economic evaluations of obesity prevention interventions incorporate considerations of scale.
The findings suggest that while many studies model the costs and impacts of interventions, few rigorously account for how real-world scale-up might affect cost-effectiveness—posing challenges for policy and investment decisions.
Led by researchers from Deakin Health Economics in Australia, the review analysed 51 primary economic evaluation studies across a wide range of interventions aimed at preventing obesity or improving related risk factors like poor diet and physical inactivity. These studies included both within-trial and modelled evaluations, covering 132 discrete interventions.
The review found significant variation in how scale was defined, measured, and incorporated—and identified a pressing need for more consistent and transparent methods to guide economic evaluations of population-level interventions.
Why scale matters
Public health interventions that work well in small-scale trials often face reduced effectiveness—or “voltage drop”—when implemented widely. At the same time, costs may change significantly due to economies or diseconomies of scale. These factors can dramatically alter the apparent value of an intervention, and if not well understood, can lead to inefficient or poorly informed policy decisions.
Despite this, the review found:
- Only three studies evaluated interventions that had actually been implemented at scale in the real world.
- Many evaluations used simplified or hypothetical assumptions about population reach, cost changes, or effectiveness
- Methods for estimating effectiveness at scale varied widely, and few studies adjusted for potential voltage drop.
- Equity considerations were rarely included, despite known disparities in obesity burden and intervention access.
Towards better economic evidence for public health
The authors argue that improving how scale is considered in economic evaluations is critical to support decision-making on obesity prevention investments. They call for the development of practical guidance for health economists, including:
- Typologies of scale-sensitive evaluation methods
- Greater use of real-world data from scaled interventions
- Integration of equity-informed analyses to assess distributional impacts
- Transparent reporting of assumptions about intervention reach, cost, and effectiveness
As countries and health systems continue to invest in upstream solutions for obesity prevention, this review highlights the urgent need for more consistent and transparent economic evidence that reflects the realities of scaling interventions in diverse settings. Ensuring evaluations are grounded in real-world complexity will help maximise impact and value for money.
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