Population-level Outcomes Research Articles

A simulation analysis to characterize the dynamics of vaccinating behaviour on contact networks

BackgroundHuman behavior influences infectious disease transmission, and numerous "prevalence-behavior" models have analyzed this interplay. These previous analyses assumed homogeneously mixing populations without spatial or social structure. However, spatial and social heterogeneity are known to significantly impact transmission dynamics and are particularly relevant for certain diseases. Previous work has demonstrated that social contact structure can change the individual incentive to vaccinate, thus enabling eradication of a disease under a voluntary vaccination policy when the corresponding homogeneous mixing model predicts that eradication is impossible due to free rider effects. Here, we extend this work and characterize the range of possible behavior-prevalence dynamics on a network.MethodsWe simulate transmission of a vaccine-prevetable infection through a random, static contact network. Individuals choose whether or not to vaccinate on any given day according to perceived risks of vaccination and infection.ResultsWe find three possible outcomes for behavior-prevalence dynamics on this type of network: small final number vaccinated and final epidemic size (due to rapid control through voluntary ring vaccination); large final number vaccinated and significant final epidemic size (due to imperfect voluntary ring vaccination), and little or no vaccination and large final epidemic size (corresponding to little or no voluntary ring vaccination). We also show that the social contact structure enables eradication under a broad range of assumptions, except when vaccine risk is sufficiently high, the disease risk is sufficiently low, or individuals vaccinate too late for the vaccine to be effective.ConclusionFor populations where infection can spread only through social contact network, relatively small differences in parameter values relating to perceived risk or vaccination behavior at the individual level can translate into large differences in population-level outcomes such as final size and final number vaccinated. The qualitative outcome of rational, self interested behaviour under a voluntary vaccination policy can vary substantially depending on interactions between social contact structure, perceived vaccine and disease risks, and the way that individual vaccination decision-making is modelled.

The Built Environment and Health: Introducing Individual Space-Time Behavior

Many studies have examined the relationship between the built environment and health. Yet, the question of how and why the environment influences health behavior remains largely unexplored. As health promotion interventions work through the individuals in a targeted population, an explicit understanding of individual behavior is required to formulate and evaluate intervention strategies. Bringing in concepts from various fields, this paper proposes the use of an activity-based modeling approach for understanding and predicting, from the bottom up, how individuals interact with their environment and each other in space and time, and how their behaviors aggregate to population-level health outcomes.

Covering the Uninsured as a Quality Improvement Strategy

Covering the Uninsured as a Quality Improvement Strategy

Assessment of the dynamics of microparasite infections in genetically homogeneous and heterogeneous populations using a stochastic epidemic model1

The aim of this paper was to explore the effect of genetic heterogeneity in host resistance to infection on the population-level risks and outcomes of epidemics. This was done using a stochastic epidemiological model in which the model parameters were assumed to be genetically controlled traits of the host. A finite locus model was explored, with a gene controlling the transmission coefficient (i.e., host susceptibility to infection) and a gene controlling the recovery period. Both genes were simulated to have 2 alleles with underlying additive or dominance inheritance and an independent assortment of alleles. The model was parameterized for a viral pig disease (transmissible gastroenteritis), and complete homogeneous mixing among genotypes was assumed. Mean population genotype dramatically affected epidemic outcomes, and subtle effects of heterogeneity on epidemic properties were also observed. Genetic variation in the transmission coefficient led to probabilities of epidemics occurring that were slightly greater than expected, but genetic variation in the recovery rate had no such effect. Epidemics were generally less severe in genetically heterogeneous populations than expected from the constituent subpopulations. Furthermore, the genotype of the initial infected animal had a marked effect on epidemic probabilities, particularly when genetic variation was for recovery rate. The results of this model provide useful information to determine the optimum population structures and to exploit genetic variation in resistance to infection. Applications of the proposed model in genetically heterogeneous populations for identifying practical disease management strategies are also discussed.

Mathematical models for HIV transmission dynamics: tools for social and behavioral science research.

HIV researchers have long appreciated the need to understand the social and behavioral determinants of HIV-related risk behavior, but the cumulative impact of individual behaviors on population-level HIV outcomes can be subtle and counterintuitive, and the methods for studying this are rarely part of a traditional social science or epidemiology training program. Mathematical models provide a way to examine the potential effects of the proximate biologic and behavioral determinants of HIV transmission dynamics, alone and in combination. The purpose of this article is to show how mathematical modeling studies have contributed to our understanding of the dynamics and disparities in the global spread of HIV. Our aims are to demonstrate the value that these analytic tools have for social and behavioral sciences in HIV prevention research, to identify gaps in the current literature, and to suggest directions for future research.

A Population-Based Study of Outcomes from Thyroidectomy in Aging Americans: At What Cost?

We wanted to evaluate clinical and economic outcomes after thyroidectomy in patients 65 years of age and older, with special analyses of those aged 80 years and older, in the US. This was a population-based study using the Healthcare Cost and Utilization Project Nationwide Inpatient Sample, 2003-2004, a national administrative database of all patients undergoing thyroidectomy and their surgeon providers. Independent variables included patient demographic and clinical characteristics and surgeon descriptors, including case volume. Clinical and economic outcomes included mean total costs and length of stay (LOS), in-hospital mortality, discharge status, and complications. There were 22,848 patients who underwent thyroidectomies, including 4,092 (18%) aged 65 to 79 years and 744 (3%) 80 years of age or older. On a population level, patient age is an independent predictor of clinical and economic outcomes. Average LOS for patients 80 years and older is 60% longer than for similar patients 65 to 79 years of age (2.9 versus 2.2 days; p < 0.001), complication rates are 34% higher (5.6% versus 2.1%; p < 0.001), and total costs are 28% greater ($7,084 versus $5,917; p < 0.001). High-volume surgeons have shorter LOS and fewer complications but perform fewer thyroidectomies for aging Americans; although they do nearly 29% of these procedures in patients younger than 65 years, they do just 15% of thyroidectomies in patients 80 years and older and 23% in patients 65 to 79 years. On a population level, clinical and economic outcomes for patients 65 years and older undergoing thyroidectomies are considerably worse than for similar, younger patients. The majority of thyroidectomies in aging Americans is performed by low-volume surgeons. More data are needed about longterm outcomes, but increased referrals to high-volume surgeons for aging Americans are necessary.

Physical Activity as Primary Prevention to Address Cancer Disparities

To review the research literature on physical activity (PA) intervention trials, with an emphasis on underserved populations. Research studies, review articles, and books. PA intervention studies have generally shown statistically significant but modest outcomes. Comprehensive intervention designs combining individual-level and physical environmental changes have posted the largest effect sizes, and emerging models are incorporating sociocultural and organizational environmental changes with promising results. Research including or targeting underserved populations poses unique challenges at each stage of the intervention process: design, recruitment, implementation, and evaluation. Synthesis of evidence-based approaches to address these challenges is presented. Promoting PA in underserved communities is essential in improving population-level cancer outcomes. Additional resources are becoming available to nursing researchers and practitioners to aid in the conduct of PA intervention in understudied groups.

Gene response profiles for Daphnia pulex exposed to the environmental stressor cadmium reveals novel crustacean metallothioneins

BackgroundGenomic research tools such as microarrays are proving to be important resources to study the complex regulation of genes that respond to environmental perturbations. A first generation cDNA microarray was developed for the environmental indicator species Daphnia pulex, to identify genes whose regulation is modulated following exposure to the metal stressor cadmium. Our experiments revealed interesting changes in gene transcription that suggest their biological roles and their potentially toxicological features in responding to this important environmental contaminant.ResultsOur microarray identified genes reported in the literature to be regulated in response to cadmium exposure, suggested functional attributes for genes that share no sequence similarity to proteins in the public databases, and pointed to genes that are likely members of expanded gene families in the Daphnia genome. Genes identified on the microarray also were associated with cadmium induced phenotypes and population-level outcomes that we experimentally determined. A subset of genes regulated in response to cadmium exposure was independently validated using quantitative-realtime (Q-RT)-PCR. These microarray studies led to the discovery of three genes coding for the metal detoxication protein metallothionein (MT). The gene structures and predicted translated sequences of D. pulex MTs clearly place them in this gene family. Yet, they share little homology with previously characterized MTs.ConclusionThe genomic information obtained from this study represents an important first step in characterizing microarray patterns that may be diagnostic to specific environmental contaminants and give insights into their toxicological mechanisms, while also providing a practical tool for evolutionary, ecological, and toxicological functional gene discovery studies. Advances in Daphnia genomics will enable the further development of this species as a model organism for the environmental sciences.

Adding the missing link back into mate choice research

Evolutionary psychologists should go beyond research on individual differences in attitudes and focus more on detailed models of psychological mechanisms. We argue for complementing attitude research with agent-based computational modeling of mate choice. Agent-based models require detailed specification of individual choice mechanisms that can be evaluated in terms of both their psychological plausibility and the population-level outcomes they produce.

Dispersal patterns among three species of squirrel monkeys (Saimiri oerstedii, S. boliviensis and S. sciureus): II. Within-species and local variation

AbstractThree long-term field studies, together with numerous supplementary sources of information, demonstrate that the Neotropical squirrel monkey, genus Saimiri (Primates: Cebidae) are distinguished among mammals by the wide divergence in dispersal patterns among congeners. Both sexes of Saimiri sciureus at Raleighvallen in the Central Suriname Nature Reserve undertake dispersal on several to many occasions during their lifetime. Male dispersal and female philopatry characterize S. boliviensis studies at Manu, Peru. Among S. oerstedii, studied at Corcovado and other locations in Costa Rica, females disperse and males are philopatric. This is the second in a series of three companion reports investigating patterns and processes relevant to dispersal in these three species of squirrel monkeys. The first report, I. Divergent costs and benefits (Boinski et al., 2005), predicts the direct and inclusive fitness costs and benefits structuring species, sex and individual dispersal strategies among squirrel monkeys. III. Cognition (Boinski, 2005), the final report comprising this monograph, considers the possible cognitive mechanisms underlying dispersal among squirrel monkeys and other taxa, and suggests useful strategies to collect and interpret additional data from laboratory and field contexts.Here we evaluate the sources and potential magnitude of variation in dispersal strategies within each squirrel monkey species. For all three congeners, local edaphic and anthropogenic regimes of habitat disturbance probably represent the major source of within-species variance in the density of wild populations. Squirrel monkey population density, all else being equal, positively increases with the intensity of habitat disturbance. New evidence suggests that in addition to edaphic and recent historical disturbance regimes, in some localities in the Neotropical lowlands anthropogenic disturbance caused by pre-Columbian Amerindians remains a potent factor enhancing squirrel monkey numbers.Squirrel monkeys are predicted to exhibit density-dependent behavioural responses. In turn, these responses are expected to modulate population-level dispersal outcomes in several predictable axes. Major between-site variation in dispersal strategies, however, is unlikely for either sex among S. oerstedii or S. boliviensis. Although all natal male S. sciureus almost certainly disperse before or at the time of sexual maturity, the proportion of females emigrating from a S. sciureus troop appears more variable, dependent on local levels of within-troop competition for food. In any year or season, those mature and immature female S. sciureus with high priority access to food resources are least likely to disperse.

Analyzing the contribution of community change to population health outcomes in an adolescent pregnancy prevention initiative.

Few evaluations of community initiatives have established a link between intermediate outcomes, such as community or systems change, and more distant population-level health outcomes (e.g., estimated rates of employment or adolescent pregnancy). This article describes an analysis of the contribution of community changes facilitated by a community health initiative to prevent adolescent pregnancy to the population-level outcome of birth rates for teens. The authors examine a hypothesis that this link might be expected when community changes are of greater amount, intensity, duration, and exposure. The results showed reductions in birth rates in Target Area A, where there was a greater concentration of community changes and a slight increase where there were far fewer changes. This report provides a method for describing empirically the contribution of environmental change to more distant population-level outcomes.

A review of collaborative partnerships as a strategy for improving community health.

Collaborative partnerships (people and organizations from multiple sectors working together in common purpose) are a prominent strategy for community health improvement. This review examines evidence about the effects of collaborative partnerships on (a) community and systems change (environmental changes), (b) community-wide behavior change, and (c) more distant population-level health outcomes. We also consider the conditions and factors that may determine whether collaborative partnerships are effective. The review concludes with specific recommendations designed to enhance research and practice and to set conditions for promoting community health.

Later-life economic inequality in longitudinal perspective.

Data from the National Longitudinal Survey of Older Men were used to estimate economic inequality within three 5-year cohorts as they moved from midlife to later life. The Gini index of inequality increased steadily after age 59, supporting the hypothesis that within-cohort inequality increases in late life. However, a transition analysis found considerable mobility in relative status for individuals over a 15-year period. These results suggest the need to develop a longitudinal perspective on later-life economic status which distinguishes between individual-level and population-level outcomes and identifies the life events and characteristics of individuals that predict changes in economic status. Further research is needed on the processes which lead to later-life inequality, and on the distributional impact of public and private pension policies.

Comparative political studies: William H. Flanigan and Nancy H. Zingale, ‘Western European and Anglo-American party systems: A dimensional analysis’, 14: 4, January 1982, pp. 481–515

Little consensus exists about how to measure quality of care in abortion. Our purpose is to (a) provide common language for healthcare quality definitions, frameworks and measurement; (b) synthesize literature about quality measurement in abortion; and (c) present criteria for quality metric development. Quality includes effectiveness, patient centeredness, timeliness, efficiency and equity of care. Information about structure, process and outcomes of care is used to measure quality. We do not have good evidence about expected population-level health and behavioral outcomes associated with improving abortion service quality. Abortion patients overwhelmingly report high satisfaction with services, but it is not clear if their satisfaction indicates high-quality care. Guidance exists for quality metric selection; measures must focus on priority topics, be scientifically sound and be feasible. Technical quality standards and clinical guidelines exist, but we lack a standard set of quality metrics. Partners in the Abortion Service Quality Initiative (https://asq-initiative.org/) are collaborating to develop the first-ever global standard for measuring abortion service quality in low- and middle-income countries, both in and out of health care facilities. Standardized and validated quality metrics would move our field forward and contribute to quality improvement activities and, ultimately, to improved health outcomes for women and families.We define quality of health care, synthesize the evidence about quality of care in abortion and advocate for standardized and validated quality metrics to improve health outcomes for women.