Onions and Bubbles: Models of the Social Determinants of Health

A generous range of models is available to explain the impact of these factors on an individual’s health. Some models resemble onions — concentric circles of variables, each construed as operating at a more distal position from the individual (3). One group provided an inverted example of the pyramid (4). The causal web (5) is another representation. These images imply linear, if bidirectional, relationships operating in two dimensions. Yet we know the true relationships are more complex. A visual model might be more meaningful if considered in three or more dimensions. Glass and McAtee observe that another image is that of a running stream, again suggesting “upstream,” “distal” factors that affect “downstream,” “proximate” factors. Their concepts offer a three-dimensional model that uses the axes of time and biologicalsocial organization (6).