The science of scaling in health

Background A pressing issue faced in public health and global health, is how to create and sustain equitable large-scale health improvement across local and national systems. In this paper, we discuss how the current emphasis in scaling centres on the act of scaling interventions and implementation processes, as opposed to the system of generalisable knowledge and enquiry that explains innovation scaling and system-wide health transformation at scale. We critically review the science of scaling – or scaling science - in physical activity, nutrition and public health broadly, drawing on examples from primary and secondary prevention. Methods A narrative review of relevant dissemination, implementation and scaling literature ( n = 81) from public, clinical, and global health, international development, and social innovation. We also drew on the authors’ combined international expertise. Results We define the science of scaling as the systematic pursuit and application of knowledge to optimise sustained equitable outcomes of innovation and scaling , minimise ineffective , low value , inequitable or harmful outcomes through down-scaling , and generate new evidence through robust methodologies , real-world research , policy , and practice. We introduce 12 core concepts structured by five higher order domains. Concepts focus on scaling: (1) mindset (2), within complex and dynamic systems, (3) across and within micro-, meso- and macro-levels, (4) beyond the health ecosystem, (5) for small-scale, large-scale and systemic change, (6) readiness, (7) politics and the politics of scaling, (8) strategies and mechanisms, (9) ethically, equitably and responsibly, (10) sustainably, (11) guidelines, theories, models, frameworks and tools, and (12) methodologies and evaluation. We provide examples and recommendations for each concept, including research questions for selected concepts. Conclusion Scaling is not always the solution to an unhealthy society, and scaling is not merely an extension of implementation. Not all evidence-based interventions can and should be scaled. The science of scaling encourages broader and deeper thinking about the structures and conditions that facilitate and hinder scaling processes, the impact of innovation scaling, and the conditions necessary for sustained and equitable change at both small and large scales. We believe the science of scaling has been overlooked and argue that this increasingly important area needs explicit attention.