The relative contribution of layers of the Social Ecological Model to childhood obesity

The Institute of Medicine’s 2005 report, Preventing Childhood Obesity: Health in the Balance, used the Social Ecological Model (SEM) to describe the possible aetiology of the childhood obesity epidemic and also to lay the groundwork for future interventions(1). Based on ecological systems theory, the SEM postulates that changes in individual outcomes are influenced not only by individual-level factors such as age and gender, but also by interactions with the larger social, cultural, economic and environmental contexts in which individuals live(2,3). Appropriately, the SEM, which posits concentric layers of influence including intrapersonal, interpersonal, community, organization, government, industry and societal domains, is a frequently used model in childhood obesity research and prevention efforts(4–6). Researchers have investigated individual factors within different layers of the SEM to understand the influence of these factors on children’s weight status. Child-level factors such as age, race and gender(7,8), parental characteristics such as weight status and education level(8–10) and household characteristics such as income(11) have consistently been associated with children’s weight status. Community-level factors such as proximity to types of food outlets and physical activity (PA) facilities, however, have produced mixed findings(12–25). Although prior studies have examined specific elements of the SEM, important unanswered questions remain about the combined contribution of elements in each layer. Such an analysis is crucial for setting priorities among different intervention domains and allocating scarce resources. For example, studies often investigate the independent contribution of one or more elements of the community built environment (e.g. parks, stores)(16,25,26), but seldom quantify the combined contribution of various elements of the built environment taken together on children’s weight status. Neglecting the combined contribution of elements within the same SEM layer can be problematic if those elements correlate highly with each other, creating a situation in which each individual element appears to contribute negligibly to weight outcomes although the elements taken together are highly predictive. Similarly, prior studies seldom account for the combined contribution of each SEM layer independent of contributions attributable to other layers. For example, in analyses where models are built incrementally, estimates of the contribution of variables entered in the first step (e.g. individual-level sociodemographic variables) do not reflect or account for contributions from subsequent layers (e.g. community-level demographics, built environment variables)(9,27). Thus examination of the independent and relative contribution of each layer of the SEM – information that can be valuable in designing interventions and setting priorities – is not possible. To address these unanswered questions, the analysis presented here uses data collected from low-income, high-minority communities as part of the New Jersey Childhood Obesity Study. The study collected comprehensive information on children’s BMI and multiple layers of the SEM (Fig. 1), including child-, parent-, household- and neighbourhood-level characteristics, parental perceptions of the food and PA environments and objective measures of community food and PA environments, to examine the unique and relative contribution of different layers on children’s weight status. Fig. 1 Social Ecological Model showing the layers influencing a child’s weight status (PA, physical activity)