We stated in an Editorial published in 2013 ¹1. Carvalho MS, Travassos C, Coeli CM. Mais do mesmo? Cad Saúde Pública 2013; 29:2141-3. (p. 2142) that “in science we cannot content ourselves with well-established approaches”. As researchers in the collective health field, we must use science to search for paths to confront the major challenges facing the health of populations. We must deepen the debate on advancing a “consequentialist” science ²2. Galea S. An argument for a consequentialist epidemiology. Am J Epidemiol 2013; 178:1185-91., whether in the field of epidemiology, the human sciences, or health policy. It is not enough to identify causal mechanisms, to understand the limits of the care provided by the Brazilian Unified National Health System (SUS), and to acknowledge the importance of individual discourse in diagnosing health problems and access to health services. All of this is extremely important, but we must take a step further and identify approaches for dealing with the complexity of these problems.

Complex is not synonymous with complicated. We see complex problems as those whose shape involves multiple relations and feedback loops that balance and guarantee the system’s dynamic stability. The question here is not to identify the cause of the growing prevalence of obesity in the world as a consequence of forces in the food industry, agribusiness, and food deserts, but how to deal with the problem ³3. Lee BY, Bartsch SM, Mui Y, Haidari LA, Spiker ML, Gittelsohn J. A systems approach to obesity. Nutr Rev 2017; 75 Suppl 1:94-106.. We would all like the Guia Alimentar para a População Brasileira⁴4. Departamento de Atenção Básica, Secretaria de Atenção à Saúde, Ministério da Saúde. Guia alimentar para a população brasileira. 2ª Ed. Brasília: Ministério da Saúde; 2014. to have a major impact on obesity prevalence. And if this impact fails to materialize, it is due precisely to the stability of a complex system.

How do we address problems that do not display a linear causal chain, in which A causes B with C as the outcome? Even the notion of “outcome” restricts our understanding in this case. The problem requires considering the whole set, with the different actors and points of view. And to confront the problem, simplification is necessary, always coherently and without losing sight of the whole, explicitly bringing to the surface the assumptions and mental models, and creating a shared vision ⁵5. Peters DH. The application of systems thinking in health: why use systems thinking? Health Res Policy Syst 2014; 12:51.. The only criterion that allows combining such different and multidisciplinary points of view, from economics to nutritional science, from epidemiology to administration of the SUS, from policy to the quality of the food available in poor communities, is action, the perspective of a coordinated intervention in an identified problem.

Various methods coexist (and even contradict each other) in this approach. Some of these methods are qualitative, described as “soft system approaches”, while others are more quantitative ⁵5. Peters DH. The application of systems thinking in health: why use systems thinking? Health Res Policy Syst 2014; 12:51.. What they all share is the need to leave our comfort zone, to simplify while ensuring that the view of the whole is lost. As researchers in the collective health field, we need to change our mental model, maintaining a stance of permanent learning ⁶6. Chekland P, Poulter J. Learning for action - a short definitive account of soft systems methodology and its use for practitioners, teachers and students. Chichester: Wiley; 2006..

There are several problem-situations in the collective health field. When we are faced with a problem (thus justifying the term “problem-situation”), what often comes to mind immediately is that a relatively simple measure “would suffice”. It would suffice to control the vector population, although “there’s no evidence that any recent vector-control interventions, including massive spraying of insecticides, have had any significant effect on...” ⁷7. Haug CJ, Kieny MP, Murgue B. The Zika challenge. N Engl J Med 2016; 374:1801-3. (p. 1802). Or that it would be possible to control hypertension by prescribing properly indicated drugs. It “would suffice” for hypertensive individuals to follow the prescription correctly, which is not always true even for persons with a university education ⁸8. Chor D, Pinho Ribeiro AL, Sá Carvalho M, Duncan BB, Andrade Lotufo P, Araújo Nobre A, et al. Prevalence, awareness, treatment and influence of socioeconomic variables on control of high blood pressure: results of the ELSA-Brasil Study. PLoS One 2015; 10:e0127382.. Why do vaccination coverage rates drop, when they are such a successful strategy for controlling numerous diseases? Are vaccines the victims of their own success? ⁹9. Baima C. "Somos vítimas do sucesso alcançado pela vacinação", diz um dos pioneiros da fabricação de imunizantes no Brasil. O Globo 2018; 10 jul. https://oglobo.globo.com/sociedade/somos-vitimas-do-sucesso-alcancado-pela-vacinacao-diz-um-dos-pioneiros-da-fabricacao-de-imunizantes-no-brasil-22869482.
https://oglobo.globo.com/sociedade/somos... .

In Brazil’s current context of setbacks in social policies, when the rejection of science is being constructed deliberately ¹⁰10. Proctor R, Schiebinger LL. Agnotology: the making and unmaking of ignorance. Stanford: Stanford University Press; 2008., it is indispensable to adopt ways to address the challenges in collective health that contribute to multidisciplinary action, combining researchers, policymakers, and the population, integrating culture, knowledge, and science. CSP hopes that the collective health community will rise to this challenge.

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