4c. Focus on Systems Theory  

What is Systems Theory? How can it guide population health interventions?

As one of your required readings notes, a key limitation of ecological models is their lack of specificity about the most important hypothetical influences on behaviour.¹ If, for example, you were asked to develop a food security strategy for your community, would you focus on a) income, b) food-related skills/knowledge, c) the built environment (e.g., reducing “food deserts”), or d) some combination of the above?

To address these prioritization challenges, public health is increasingly reliant on systems theory. Systems theory is premised on the notion that the function of complex systems (including the micro and macro environments where health behaviours take place) are dependent upon interactions between heterogeneous elements that cannot be fully understood by examining these elements in isolation of one another.² Over the past decade, public health has begun to apply systems theory methods to shape programs and policies for a range of priorities from pandemic planning to comprehensive tobacco control.^3,4

Learn more about systems theory and its application to health issues from the following video:

The Causal Loop Diagram

Systems research in public health is guided by a range of methods. One of the most widely used tools in systems theory research is a causal loop diagram, a visual aid illustrating the inter-connectivity of key factors contributing to a health issue. The relationships between these variables, which are most often represented by arrows, can be labelled as positive or negative.⁵

The guide to creating causal loop diagrams (PDF), developed by the Mailman School of Public Health at Columbia University, gives an example of a causal loop diagram that illustrates the range of social, economic, technological, and behavioural factors contributing to neonatal mortality in Uganda.⁶

By illustrating the complexity and inter-relatedness of factors affecting this public health issue, the causal loop diagram serves as a cautionary note against relying on any single intervention. Just as there is no single, over-arching causal factor for neonatal mortality in Uganda, no single intervention is likely to have a substantive impact if it’s implemented in isolation from other complementary interventions. Rather, a systems approach is needed to guide the identification of key points for intervention and the development of complementary strategies. 

Balancing Clarity and Complexity: Systems-Level Causes of Child Obesity

While the application of systems theory tools, such as causal loop diagrams, can help to shed clarity on the relationship between the wide range of socio-environmental factors contributing to population health issues, it can also result in diagrams with daunting levels of detail and complexity, especially for multi-layered “wicked problems” like childhood obesity.

In 2007, as part of its Foresight Programme, which focused on finding innovative solutions to complex health and social problems, the Government Office for Science in the United Kingdom commissioned a report outlining a long-term (40-year) vision of how the United Kingdom could respond to the growing problem of obesity.⁷ The report authors created a causal loop diagram to better understand the complex systemic structure of obesity and to assist policy makers with defining and testing possible policy options to respond to obesity.

Read more about the process they undertook to create the causal loop diagram in the report: Tackling Obesities: Future Choices — Building the Obesity System Map (PDF). The resulting diagram is shown below.

The level of complexity in this diagram led many in the public health sector to label it as the "spaghetti map" of obesity. What do you think of this diagram? If you were using it to develop an ecological intervention to prevent obesity in your community, would it be more likely to help or hinder your planning efforts?

One of the critiques of the Foresight approach is that it utilized a “top-down,” expert-led approach, contravening the core tenet of community engagement underlying most environmental/ecological theories of population health.

However, a more participatory, community-driven approach to identifying system-level causes of child obesity led by a team of Australian researchers in 2014 yielded a causal loop diagram of equal complexity.⁸ Their diagram, published in A Community Based Systems Diagram of Obesity Causes, which documents the inter-relatedness of social influences, fast food and junk food, participation in sport, and general physical activity resulted in another variation of the UK “spaghetti map.”

The complexity of such diagrams has led some experts to try to reduce their elements to fewer priority variables for action.⁹ However, such an approach runs the risk of being overly reductionist by omitting factors that may play an essential role in the chain of causation.

While the application of systems theory tools help to elucidate the relationships between the myriad of socio-environmental causes contributing to complex issues like child obesity, they do not provide “short cuts” for the amount of time and effort required to carefully review these inter-relationships and identify appropriate, evidence-based opportunities for intervention. This is a key point to keep in mind as you develop your iterative assignment frameworks.