Complex systems thinking and current impasses in health disparities research

Abstract

Complex systems approaches have received increasing attention in public health because reductionist approaches yield limited insights in the context of dynamic systems. Most discussions have been highly abstract. There is a need to consider the application of complex systems approaches to specific research questions. I review the features of population health problems for which complex systems approaches are most likely to yield new insights, and discuss possible applications of complex systems to health disparities research. I provide illustrative examples of how complex systems approaches may help address unanswered and persistent questions regarding genetic factors, life course processes, place effects, and the impact of upstream policies. The concepts and methods of complex systems may help researchers move beyond current impasse points in health disparities research.

FIGURE 1

The interplay of genes and environments: recursive developmental remodeling. Note. A single-headed arrow from X to Y indicates that X is a cause of Y or that X causes increased exposure to Y. A line intersecting a 1-headed arrow (in the form of a T) indicates that the factor modifies or modulates the relation between X and Y (effect modification in epidemiologic terms). The T-shaped line from structural/physiological changes that intersects the arrow from environment to gene expression indicates that the structural and physiological changes modify or modulate the effect of environments on gene expression. Positive or negative feedback loops are indicated with an R (reinforcing) or a B (balancing). Reinforcing loops promote or reinforce change in one direction. Balancing loops tend to close the gap between the current state and the desired state. Directionality (plus or minus signs associated with the arrows) is not indicated in the figures but the types of relations can be inferred from the description in the text. Source. Adapted from Cole.

FIGURE 2

The interplay of genes and environment: the role of gene–environment interaction and correlation. Note. A single-headed arrow from X to Y indicates that X is a cause of Y (e.g., family norms are causally related to physical activity) or that X causes increased exposure to Y (e.g., genetic factors related to exercise predisposition affect selection into exercise-promoting environments). A line intersecting a 1-headed arrow (in the form of a T) indicates that the factor modifies or modulates the relation between X and Y. Positive or negative feedback loops are indicated with an R (reinforcing) or a B (balancing).

FIGURE 3

Long-term effects and transgenerational transmission of early life experiences. Note. A single-headed arrow from X to Y indicates that X is a cause of Y or that X causes increased exposure to Y. A line intersecting a 1-headed arrow (in the form of a T) indicates that the factor modifies or modulates the relation between X and Y. Positive or negative feedback loops are indicated with an R (reinforcing) or a B (balancing). Source. Based on Diorio and Meaney and Weaver et al.

FIGURE 4

Dynamic relations between health and socioeconomic circumstances over the life course and across generations. Note. A single-headed arrow from X to Y indicates that X is a cause of Y or that X causes increased exposure to Y. A line intersecting a 1-headed arrow (in the form of a T) indicates that the factor modifies or modulates the relation between X and Y. Positive or negative feedback loops are indicated with an R (reinforcing) or a B (balancing).

FIGURE 5

Dynamic relations between area factors, individual-level factors, and health outcomes. Note. A single-headed arrow for X to Y indicates that X is a cause of Y or that X causes increased exposure to Y. A line intersecting a 1-headed arrow (in the form of a T) indicates that the factor modifies or modulates the relation between X and Y (e.g., discrimination modifies the relation between personal resources/preferences and residential location, and stress modifies the relation between location of services and behaviors). Positive or negative feedback loops are indicated with an R (reinforcing) or a B (balancing). Reinforcing loops promote or reinforce change in one direction. Balancing loops tend to close the gap between the current state and the desired state (e.g., increases in stress result in health behaviors that reduce stress levels bringing the body back into its desired state).