Dividuals in the system.3 For example, risk of HIV infection largely depends, not only on risk behavior, but also on the prevalence of HIV infection in the community. Relationships in a system may be recursive with positive feedback loops (in which an element exerts an influence that amplifies a prior deviation) and negative feedback loops (in which an element exerts an influence that corrects a prior deviation and leads to the initial state). They may contain butterfly effects (a weak input that reverberates throughout a whole system) and random coupling (unexpected processes and outcomes from an input). Considering these processes facilitates the development of interventions that produce synergistic positive effects (e.g., providing combined services potentiates the effect of each service to reach individuals) and avoid negative homeostatic effects (e.g., individuals returning to baseline risk behavior after receiving repeated negative HIV test results.) Systems tend toward entropy, that is, outputs diminish over time without additional inputs. Thus, most interventions produce diminishing effects without the allocation of additional reinforcement or resources. Finally, many complex changes are difficult to reverse. Irreversibility does not imply that structural factors cannot be adjusted to benefit the affected communities. Rather, it means that once a structural property in a complex system develops, interventions should provide alternative configurations rather than trying to “un-develop” it. This principle has implications for intervention design. For example, socially disadvantaged communities may not recover from the effects of poverty by simply receiving material resources. As another example, HIV prevalence rates in a community can be reduced but not reversed. That is, interventions can help to reduce incidence rates, assist those already affected, and work with communities to help them to reorganize and cope with the effects of the AIDS epidemic in the long term. To summarize, in using a systems approach to analyze structural factors and develop interventions to affect behavioral outcomes, key questions may include how ARA290 web theNIH-PA Author Manuscript NIH-PA Author Manuscript NIH-PA Author ManuscriptAIDS Behav. Author manuscript; available in PMC 2011 December 1.Latkin et al.Pagerelationships among elements in the system (i.e., organizations, individuals) influence those elements, and how structural factors (e.g., resources, social organization and controls, material culture and settings) intersect with those elements to affect HIV-related behaviors. Specifically, what are the feedback loops that can potentiate the results of an intervention; what is the strength of coupling between T0901317MedChemExpress T0901317 connections or within and across systems elements; and what systems configurations are irreversible and how can new configurations be created to reduce risk? Model Levels Structural models of health outcomes describe “levels” of factors to refer to the breadth, immediacy, and degrees of individual control or influence.35,36 These levels are typically labeled “macro,” “meso,” and “micro” levels. “Macro” level structures refer to sociopolitical, economic and cultural context, and social institutions that shape social organizations with the broadest reach,8,15,21 such as by changing political structures and policies or redistributing resources. Examples of macro-level HIV-related structural interventions have included legislative changes (e.g., efforts to.Dividuals in the system.3 For example, risk of HIV infection largely depends, not only on risk behavior, but also on the prevalence of HIV infection in the community. Relationships in a system may be recursive with positive feedback loops (in which an element exerts an influence that amplifies a prior deviation) and negative feedback loops (in which an element exerts an influence that corrects a prior deviation and leads to the initial state). They may contain butterfly effects (a weak input that reverberates throughout a whole system) and random coupling (unexpected processes and outcomes from an input). Considering these processes facilitates the development of interventions that produce synergistic positive effects (e.g., providing combined services potentiates the effect of each service to reach individuals) and avoid negative homeostatic effects (e.g., individuals returning to baseline risk behavior after receiving repeated negative HIV test results.) Systems tend toward entropy, that is, outputs diminish over time without additional inputs. Thus, most interventions produce diminishing effects without the allocation of additional reinforcement or resources. Finally, many complex changes are difficult to reverse. Irreversibility does not imply that structural factors cannot be adjusted to benefit the affected communities. Rather, it means that once a structural property in a complex system develops, interventions should provide alternative configurations rather than trying to “un-develop” it. This principle has implications for intervention design. For example, socially disadvantaged communities may not recover from the effects of poverty by simply receiving material resources. As another example, HIV prevalence rates in a community can be reduced but not reversed. That is, interventions can help to reduce incidence rates, assist those already affected, and work with communities to help them to reorganize and cope with the effects of the AIDS epidemic in the long term. To summarize, in using a systems approach to analyze structural factors and develop interventions to affect behavioral outcomes, key questions may include how theNIH-PA Author Manuscript NIH-PA Author Manuscript NIH-PA Author ManuscriptAIDS Behav. Author manuscript; available in PMC 2011 December 1.Latkin et al.Pagerelationships among elements in the system (i.e., organizations, individuals) influence those elements, and how structural factors (e.g., resources, social organization and controls, material culture and settings) intersect with those elements to affect HIV-related behaviors. Specifically, what are the feedback loops that can potentiate the results of an intervention; what is the strength of coupling between connections or within and across systems elements; and what systems configurations are irreversible and how can new configurations be created to reduce risk? Model Levels Structural models of health outcomes describe “levels” of factors to refer to the breadth, immediacy, and degrees of individual control or influence.35,36 These levels are typically labeled “macro,” “meso,” and “micro” levels. “Macro” level structures refer to sociopolitical, economic and cultural context, and social institutions that shape social organizations with the broadest reach,8,15,21 such as by changing political structures and policies or redistributing resources. Examples of macro-level HIV-related structural interventions have included legislative changes (e.g., efforts to.
