Rooted in general systems theory, the social ecological perspective is a conceptual framework that focuses on the interrelationships between people and their environments. While there are many variants of the social ecological perspective [see (1
)], two principles unite them. The first principle is that human health results from the complex interaction of personal factors and multiple aspects of physical and social environments. In addition to biological, psychological, and behavioral factors, health is influenced by geography, architecture, culture, economics, politics, and social relationships (5
). In the social ecological perspective, the multiple factors that influence health are described as “levels of influence” and depicted as nested concentric circles representing contextual layers of increasing scope (eg, intrapersonal, interpersonal, organizational, community, and macro-level policy) (1
The second principle is that the multiple factors that influence health are interdependent—that is, they mutually influence each other. Interdependence holds three important implications for multilevel interventions. The first implication is that causal influence does not flow in only one direction. Physical and social features of the environment influence people’s behavior and therefore their health; at the same time, people can influence their health by modifying physical and social features of their surroundings. The second implication is that determinants at one level of influence can modify the effects of determinants at another level. Stokols [(6
), page 286] notes, for example, that “the same environmental conditions … may affect people's health differently, depending on their personalities, perceptions of environmental controllability, health practices, and financial resources.” The third implication is that changes at one level of influence can bring about changes at another level of influence. For example, changes in macro-level policy (eg, reimbursement) can stimulate changes in health-care organizations (eg, provision of patient navigation), which, in turn, can bring about changes in patient behavior (eg, timely follow-up on abnormal screening results) and outcomes (eg, diagnostic resolution). Likewise, cancer health disparities can prompt the mobilization of advocacy groups and health-care organizations to seek policy-level changes to improve access or quality.
On the basis of these principles, proponents of the social ecological view contend that multilevel interventions should be more effective than single-level interventions in changing health behavior and outcomes (1
). Smoking, for example, is influenced by multiple interdependent factors operating at different levels of influence. Thus, a multilevel intervention that combines smoking cessation counseling (an intrapersonal-level intervention) and workplace smoke-free policies (an organizational-level intervention) should be more effective than either intervention alone. However, both proponents and critics acknowledge that more interventions do not necessarily translate into more effect [eg, (5
)]. Workplace smoking bans, for example, could harden smokers’ attitudes and undercut their intentions to quit, making them less likely, not more, to take advantage of smoking cessation counseling programs. The key to designing effective multilevel interventions is to select and combine interventions that work together in complementary or synergistic ways.
Despite widespread agreement on this point, little discussion has occurred about how, when, or why interventions at different levels of influence produce (or could produce) complementary or synergistic effects. Consequently, multilevel intervention designers can find little practical advice for deciding which interventions to combine, and why. Proponents of the social ecological perspective have offered advice for choosing the level at which to intervene and for choosing among intervention options. For example, intervention efforts should focus on “high-leverage” factors—that is, those personal and environmental factors that research indicates have a disproportionate influence on the specific health issue in question (5
). Furthermore, interventions should be theoretically grounded, evidence based, economically feasible, and consistent with community values and priorities (5
). Although these criteria are useful for narrowing intervention options, they do not indicate which interventions are likely to work together in mutually reinforcing ways, and which are not.
Similarly, proponents of the social ecological perspective have offered advice on the sequencing of interventions. For example, Sallis et al. (10
) argue that environmental interventions should be put into place before educational interventions to avoid promoting unrealistic health behavior (eg, walking in high-crime areas). Likewise, Spence and Lee (12
) note that creating walking trails in a community populated predominantly with older adults might not be effective until the joint pain that many residents experience is overcome. Although such advice is useful for guiding the deployment of interventions (an implementation issue), it has limited value for guiding the selection of interventions in a multilevel intervention (a design issue).
In sum, the social ecological perspective offers a comprehensive framework for understanding the multiple interacting determinants of health. Moreover, it provides a compelling basis for the development, testing, and use of multilevel interventions that systematically target mechanisms of change at multiple levels of influence. However, in its present state of development, this perspective imparts little guidance about how to select interventions at different levels that produce (or could produce) complementary or synergistic effects. Without some framework for thinking about how interventions interact in mutually reinforcing ways, multilevel intervention designers run the risk of combining interventions that produce scattered, redundant, or mutually opposing effects (14
). To address this issue, we employ a causal modeling framework to explore five strategies for combining interventions at multiple levels that help describe when synergy and complementarity may be produced. The five strategies are accumulation, amplification, facilitation, cascade, and convergence.