Simulating syndemic risk: Using system dynamics modeling to understand psycho-social challenges facing women living with and at-risk for HIV

Best practices in system dynamics model development call for application of a multi-stepped, iterative procedure involving problem identification, system conceptualization, model formulation, model simulation, and model evaluation. This procedure unfolds differently for each model-building project, with some steps requiring more investment than others depending on the problem of focus, the availability of supportive data and information, and the targeted audience or "users" of the model. In this chapter we describe how we built and validated a system dynamics model of syndemic risk among women living with and at-risk for HIV in a low-resource, urban environment. We explain how we applied three sources of evidence to the model-building process, underscoring key decision-points we encountered along the way. We use the model to illustrate divergent patterns of syndemic risk using simulated profiles. These profiles generated important insights and implications for designing clinical, community, and public health interventions for this vulnerable population, including providing a deeper understanding of the dynamics of syndemic risk. Specifically, our model emphasized the need for individualized multi-aimed psychosocial interventions, prioritizing safety planning and substance abuse treatment, while addressing unmet psychosocial challenges and maximizing resilience. Finally, we reflect on how every system dynamics model-building project is informed by a process of careful deliberation by the modelers and their participating stakeholders, with the desired outcome of a deeper understanding of the problem and ways to effectively address it.