The need for a complex systems model of evidence for public health

Abstract

Despite major investment in both research and policy, many pressing contemporary public health challenges remain. To date, the evidence underpinning responses to these challenges has largely been generated by tools and methods that were developed to answer questions about the effectiveness of clinical interventions, and as such are grounded in linear models of cause and effect. Identification, implementation, and evaluation of effective responses to major public health challenges require a wider set of approaches 1,2 and a focus on complex systems. 3,4 A complex systems model of public health conceptualises poor health and health inequalities as outcomes of a multitude of interdependent elements within a connected whole. These elements affect each other in sometimes subtle ways, with changes potentially reverberating throughout the system. 5 A complex systems approach uses a broad spectrum of methods to design, implement, and evaluate interventions for changing these systems to improve public health.Complex systems are defined by several properties, including emergence, feedback, and adaptation. 3 Emergence describes the properties of a complex system that cannot be directly predicted from the elements within it and are more than just the sum of its parts. For example, the changing distribution of obesity across the population can be conceptualised as an emergent property of the food, employment, transport, economic, and other systems that shape the energy intake and expenditure of individuals. Feedback describes the situation in which a change reinforces or balances further change. For example, if a smoking ban in public places reduces the visibility and convenience of smoking, and this makes it less appealing, fewer young people might then start smoking, further reducing its visibility, and so on in a reinforcing loop. Adaptation refers to adjustments in behaviour in response to interventions, such as a tobacco company lowering the price of cigarettes in response to a public smoking ban.Rhetoric urging complex systems approaches to public health is only rarely operationalised in ways that generate relevant evidence or effective policies. 1,6 Public health problems that emerge as a property of a complex system cannot necessarily be solved with a simple, single intervention, but the interacting factors within the system can potentially be reshaped to generate a more desirable set of outcomes. 7,8 Achievement of meaningful impacts on complex multicausal problems, like obesity, requires more than single interventions, such as traffic light food labelling or exercise on prescription, many of which require high levels of individual agency, have low reach and impact, and tend to widen health inequalities. 9-11 Shifts within multiple elements across the many systems that influence obesity are required, some of which might only have small effects on individuals but can drive large changes when aggregated at population level. 12 Although randomised controlled trials of individual-level interventions are relatively strai...

Promoting a healthy cities agenda through indicators: development of a global urban environment and health index

“…However, research methods and study designs and sizes have not been sufficient to support strong causal associations between many attributes in the built environment and their health outcomes (Sarkar et al 2015). Furthermore, the range of factors which interact within the urban environment to impact health are recognised as forming a complex system (Northridge et al 2003, Galea and Vlahov 2005, Rydin et al 2012) and epidemiological and public health research methods are not well-equipped to unpick this complexity (Rutter et al 2017). Notwithstanding weaknesses in the evidence base and challenges due to the complexity of urban health, researchers such as Grant et al (2017) and Rydin et al (2012) have argued that built environment policy-makers and practitioners should not hold back on planning and designing healthy cities using the bestavailable evidence.…”

Towards a critical complex systems approach to public health

“…There are growing calls for public health research to eschew linear models of cause and effect typical of clinical research, and instead to embrace approaches that recognise the manifold, multi-layered and interdependent processes that produce patterns of poor health (Rutter et al, 2017). This recent 'complexity turn' in public health is overdue, desperately needed and to be welcomed.…”

“…A characteristic of complex systems, which advocates of this approach are often at pains to point out, is their 'emergent' nature. Rutter et al (2017), for example, note that 'emergence describes the properties of a complex system that cannot be directly predicted from the elements within it and are more than just the sum of its parts' . This has been long recognised in decades of social and political theory that identifies repeating patterns at the level of systems.…”

A Conceptual Framework for Chronic Disease Prevention Based on Multilevel Approach

“…Regarding the alternatives, until last decades, health systems traditionally focused on a rather individualistic approach with a narrow approach having the disease in the centre. Modern public health introduced the issues of complexity and system science (de Montigny, Desjardins, & Bouchard, 2017;Rutter et al, 2017;Salway & Green, 2017)fully justifying the multilevel approach. In fact, there is no alternative to such approach!…”