Systems can be small or large and often coincide with the levels defined in an ecological model. For example, a school can be thought of as a micro-system within a larger community; as a meso-system within the even larger national, political, and social milieu; or as a macro-system within a global-system context. This section provides several examples of how systems thinking pertains to public health problems: body mass index (BMI) screening in schools, tobacco control in the United States, obesity modeling in the United States, and obesity prevention in the United Kingdom.
The monitoring of childhood growth has been a contentious issue for several decades (James and Lobstein, 2009). In recent years, school districts have been under pressure to respond to the childhood obesity epidemic. Despite limited evidence on the value of schools providing individually directed help for children with higher BMIs, the establishment of school-based surveillance to document obesity prevalence and to inform the development of prevention and treatment policies has been recommended (e.g., Massachusetts Department of Public Health, 2009). Although the measurement of weight and height within schools appears relatively simple and in fact has been taking place for decades, the development of rigorous measurement and reporting protocols has been limited until recently. This lack of a well-defined process, together with the failure to take a systems perspective, can result in a number of unintended consequences and perturbations to the system. For example, children may feel embarrassed or stigmatized during the process, parents may feel unequipped to act on the information they receive, health care providers in the community may not be educated about obesity treatment, the community may lack adequate pediatric programming to which children can be referred, and schools may forego other screening programs to make room for BMI screening (for example, hearing and vision screenings were cut back when the Massachusetts Public Health Council voted to require BMI screening of schoolchildren [Mullen, 2009]). In addition, although obesity rates may be high, insufficient funds or a lack of political will may prevent the school system from accessing the funding and assistance needed to address these unintended consequences, leaving the community feeling frustrated and helpless.
Although historically the tobacco control movement targeted individuals and their behaviors, it evolved into a multilevel systems approach to the problem (Abrams, 2007). Clearly, individual behavior change was the goal, but strategies involving industry, legislation, public health programming and messaging, and the health care system worked together to create that change. None of the strategies implemented as part of the movement worked alone. State by state, it was demonstrated that a combi-