Anthropometric variability in the USA: 1971-2002.

AIM: The study analysed variability in physical stature, weight, and body mass index (BMI) in the USA during 1971-2002. SUBJECTS: Subjects were non-Hispanic Blacks and Whites, 2-74 years of age from the National Health and Nutrition Examination Surveys (NHANES I-III and 1999-2002). METHODS: The coefficient of variation and the standard deviation of the logarithm of stature, weight, and BMI were used to assess anthropometric variability for groups defined by age, race, sex, income, and survey year. Weighted ordinary least squares regressions were used to estimate the effect of socio-economic variables on anthropometric variability. RESULTS: (a) The relation between age and variability in weight or BMI resembles an inverted U, (b) men have lower variability in BMI than women, (c) Blacks and the poor have greater variability in weight and BMI than Whites or than the non-poor, and (d) variability in anthropometric indices increased during 1971-2002. Results were robust to the measure of variability used and to the use of the mean and mean square of the anthropometric indicators as explanatory variables. CONCLUSION: Since anthropometric indices correlate reliably with canonical indicators of well-being (e.g. income), growing variability in anthropometric indices, particularly among the Blacks and the poor, signals growing inequality in quality of life--a worrisome trend.

The role of seasonality in the dynamics of deer tick populations.

In this paper, we formulate a nonlinear system of difference equations that models the three-stage life cycle of the deer tick over four seasons. We study the effect of seasonality on the stability and oscillatory behavior of the tick population by comparing analytically the seasonal model with a non-seasonal one. The analysis of the models reveals the existence of two equilibrium points. We discuss the necessary and sufficient conditions for local asymptotic stability of the equilibria and analyze the boundedness and oscillatory behavior of the solutions. A main result of the mathematical analysis is that seasonality in the life cycle of the deer tick can have a positive effect, in the sense that it increases the stability of the system. It is also shown that for some combination of parameters within the stability region, perturbations will result in a return to the equilibrium through transient oscillations. The models are used to explore the biological consequences of parameter variations reflecting expected environmental changes.

The precautionary principle in environmental science.

Environmental scientists play a key role in society's responses to environmental problems, and many of the studies they perform are intended ultimately to affect policy. The precautionary principle, proposed as a new guideline in environmental decision making, has four central components: taking preventive action in the face of uncertainty; shifting the burden of proof to the proponents of an activity; exploring a wide range of alternatives to possibly harmful actions; and increasing public participation in decision making. In this paper we examine the implications of the precautionary principle for environmental scientists, whose work often involves studying highly complex, poorly understood systems, while at the same time facing conflicting pressures from those who seek to balance economic growth and environmental protection. In this complicated and contested terrain, it is useful to examine the methodologies of science and to consider ways that, without compromising integrity and objectivity, research can be more or less helpful to those who would act with precaution. We argue that a shift to more precautionary policies creates opportunities and challenges for scientists to think differently about the ways they conduct studies and communicate results. There is a complicated feedback relation between the discoveries of science and the setting of policy. While maintaining their objectivity and focus on understanding the world, environmental scientists should be aware of the policy uses of their work and of their social responsibility to do science that protects human health and the environment. The precautionary principle highlights this tight, challenging linkage between science and policy.

Transient dynamics and early diagnostics in infectious disease.

To date, mathematical models of the dynamics of infectious disease have consistently focused on understanding the long-term behavior of the interacting components, where the steady state solutions are paramount. However for most acute infections, the longterm behavior of the pathogen population is of little importance to the host and population health. We introduce the notion of transient pathology, where the short-term dynamics of interaction between the immune system and pathogens is the principal focus. We identify the amplifying effect of the absence of a fully operative immune system on the pathogenesis of the initial inoculum, and its implication for the acute severity of the infection. We then formalize the underlying dynamics, and derive two measures of transient pathogenicity: the peak of infection (maximum pathogenic load) and the time to peak of infection, both crucial to understanding the early dynamics of infection and its consequences for early intervention.

Let the numbers speak.

Although it is often claimed that statistical techniques are ways of letting the objective data speak for themselves, in both the contrast and correlational modes of statistical inference, all the real work is done by the a priori decisions imported into the analysis--which categories are to be used to create contrasting populations, which categories are to be measured, which categories are to be held constant while others are compared, and which is cause and which is effect? The authors explore here the problem of directionality of causation and the relationship between cause and effect, on the one hand, and dependent and independent variables, on the other. In systems of any complexity there are feedbacks--negative and positive feedbacks forming loops, embedded in larger contexts and subject to influences that can impinge on the loop at any point, such that the same pair of variables may show positive correlations in some situations and negative correlations in others.

Models for regional heartwater epidemiology in a variable environment.

A model of the epidemic dynamics of heartwater within a cattle production unit was presented by Yonow et al. (1998). Here, the model is expanded to a region consisting of several farms to study the effect of environmental variability on control strategies. We have shown that: * In a region, where the environment of each farm is modelled with constant epidemiologic parameter values, while the between-farm parameter values differ, regional variation in the removal rate of infected cattle increases the average fraction of infected cattle across the region, while regional variation in the transmission rate of infection from ticks to cattle decreases the average fraction of infected cattle, thereby requiring control measures that keep the removal rate uniform and the transmission rate variable. * In a region, where in addition to regional variation between farms, the epidemiologic parameters of each farm are time-variant, then temporal variation in both the transmission rate and removal rate increases the average fraction of infected cattle across the region, thereby requiring control measures that keep both parameters uniform.

Toward an ecosocial view of health.

The changing patterns of health in the United States justify both celebration and dismay. We can celebrate declining mortality rates, increased life expectancy, and improvements in diagnostic and therapeutic technologies. But public health was caught by surprise by the return of infectious disease; the gap in health outcomes between rich and poor and between whites and blacks increases; there is a growing discrepancy between what is technically possible and the actual health status; and despite its greater expenditures on health, the United States lags behind the other developed countries in health outcomes. The authors examine four reasons for this: we do not buy more health care, only pay more for it; we receive more health care, but much of it inappropriate, ineffective, or harmful; only some of us get more health care; and we have created a way of life that makes us sick, then spend more to repair the damage. Major failures arise when problems are understood too narrowly. An ecosocial perspective attempts to look at the whole. It rejects as false the dichotomies social/biological, physical/psychological, genetic/environmental, lifestyle/environment, examining their interrelations rather than assigning them relative weights. In addition to looking at average differences among populations, the authors examine patterns of variability in health outcomes.

The island syndrome in rodent populations.

Populations of rodents isolated on islands often show systematic differences in demography, reproduction, behavior, and morphology when compared to mainland populations. These differences, termed the island syndrome, include higher and more stable densities, better survival, increased body mass, and reduced aggressiveness, reproductive output, and dispersal. We synthesize information in the literature on island rodent populations and construct a conceptual model to explain the island syndrome. Population density and other manifestations of the island syndrome are predicted to increase with island isolation and to decrease with island area. The effect of isolation is direct by limiting dispersal, while the effect of area is less direct. As area increases, predators, competitors, and habitat structure increase in diversity. We suggest that the intensity or absence of density-depressing factors (primarily predation in communities comprised of only a few morphologically and trophically divergent species) is primarily responsible for the area effect and serves as a principal factor differentiating island from mainland populations of rodents. Other characteristics associated with the island syndrome may be the result of both short-term and long-term processes or responses. Short-term responses include reproductive, body size, and behavioral changes that may be phenotypic reaction norms in response to higher island densities. Thus, higher densities lead to reduced reproductive output, which then leads to greater body size. Initial behavioral differences may be owing to better survival and reduced dispersal, which result in less population turnover, greater neighbor familiarity, and less aggression. Long-term changes may be due to directional selection for reduced dispersal, increased body size in response to increased intraspecific competition, reduced reproductive output (smaller litters and delayed maturation) in response to reduced mortality schedules, and reduced aggressiveness. While the model is specific to rodent populations, the conclusions may be applicable to other systems if characteristics such as body size, vagility, and community composition are considered.

Beyond our means: patterns of variability of physiological traits.

Epidemiologists usually employ measures of variability of physiological traits such as blood pressure and cholesterol only to determine confidence intervals or statistical significance. For evolutionary biologists population variability per se has proven of interest. This article explores the applicability of this perspective to the analysis of human physiology, using data from the Framingham Heart Disease Study and the National Health and Nutrition Examination Surveys. The nonrandom patterns of variability observed suggest that examination of the degree and pattern of heterogeneity within a population may provide information not evident from the analysis of mean values.

Regional Coexistence of Species and Competition between Rare Species.

A model is developed for the coexistence and exclusion of species over a region of similar habitable patches. Since the balance of local extinction and colonization would leave some patches unoccupied even without competitors, species may coexist even when all the patches are the same. Regional competition coefficients are found when species affect the local extinction or migration rates of each other. Rare species can regulate each other and even exclude other species completely.