Nonidentifiability of competing risks

Frequently one is interested in examining the survival experience of a set of individuals exposed to k risks. If W is the time of failure for the individual and J is the indicator variable for cause of death, then the competing risk framework assumes that W = min X_i and J = j if X_j is the minimum, where the X_i's are the survival lifetimes when only risk R_i is operating on the population. To examine the underlying structure of the survival experience one has to know the joint distribution of the $\text{X}{}_{\mathrm{i}}\text{(F}{}_{\mathrm{<mtext>x</mtext>}}\text{)}$. It is shown here that if only W and J are observed, the joint distribution of the $\text{X}{}_{\mathrm{i}}\text{(F}{}_{\mathrm{<mtext>x</mtext>}}\text{)}$ is nonidentifiable.     

Branching processes, Markov chains, and competing risks

This paper re-proves and generalizes results by Hardin and Sweet on the time to absorption in certain Markov chains by using a theorem on the time to extinction in multitype branching processes. Renaming “absorption” as “death” and “state immediately before absorption” as “cause of death” makes possible an interpretation in terms of competing risks. This is of very limited value, however, due to the rather severe mathematical restrictions on the Markov chains at hand.     

On the evaluation of biological hazards and competing risks

After some general remarks, and a brief explanation of Clifford's non-identifiability results for illness-death models, an attempt is made to view the competing-risk problem more biologically. The cause and time of death vary from individual to individual because they have different genetically determined susceptibilities and different life histories. Although one could define potential lifetimes associated with causes of death, averaging over different genetic susceptibilities means that from population data one cannot estimate the distribution of cause specific life spans in individuals with the same genetic susceptibility. In particular, the hazard curves for different genetic states cannot be resolved from population data.     

Stochastic mortality theory and the mortality potential: A biophysical model for certain competing risks

The theory of competing risks cannot be based entirely on the analysis of postmortem pathology data. It is necessary also to know the prevalence and residence times of the diseases in question, separately and jointly, in the living population at risk. It is also necessary to have a conceptual model of the transition process from health to disease, or from one disease state to another, within the organism, so that the formal transition probabilities estimated from epidemiological data can be interpreted in biophysical terms as arising from changes in the physico-chemical state of the organism. This paper offers such a model for transition processes arising from fluctuations of physiological state (for example, lapse into diabetic coma or insulin shock as a result of extreme high or low excursions of the blood sugar level). A Gaussian fluctuation process is postulated, and the transition probability, or incidence rate, is calculated as the frequency with which the state variable fluctuates beyond a specified distance, Λ, from the mean state. An explicit solution is given for the limiting, but biologically reasonable, case that such an excursion is a rare event. In this case, the transition probability varies exponentially for linear displacement of Λ or of the dispersion of fluctuations, σ. If Λ decreases, and/or σ increases, as a linear function of age, this model yields an exponential (Gompertzian) relation of disease incidence to age. Generalization to more than one variable is accomplished by introducing the concept of a mortality potential surface, in which the disease transitions are geometrized as saddle points, or “passes”, on the surface.     

Regression analysis of censored survival data with extensions to include competing risks and case-control studies

Statistical methods for the analysis of censored time-to-response data are reviewed. Estimation of the effect of dose levels and other regressor variables on time to response is emphasized. Both log-linear and proportional hazards regression models are discussed and illustrations are given. Methods based on the proportional hazards model are extended to competing risks and case-control studies. The competing risks generalization leads to the estimation of cause-specific regression coefficients without placing restrictions on the interrelation among failure types.     

Dependent competing risks: Bounds for net survival functions with fixed crude survival functions

Using the formulation of latent failure times, the problem of inference on survival time in the presence of competing risks is discussed. Even for the simplified problem where dose and other covariates are fixed, it is not well known that the distributions of the latent failure times are not identifiable from the usual competing risks data. Bounds for the joint survival function and marginal survival functions for the latent failure times are given, and an example illustrates the determination of empirical bounds that estimate the true bounds. In general, the bounds are wide and therefore not very useful. Some alternate approaches are briefly mentioned.     

Energy futures and green chemistry: competing for carbon

Global energy demand is expected to increase from the current 400 ExaJ per year to as much as 700–1,000 ExaJ per year by the middle of this century. If fossil carbon resources continue to make up the bulk of the energy supply, not only will atmospheric carbon dioxide increase to levels not seen for the past 30–35 million years, but depleting fossil carbon resources will become increasingly less available for other purposes, particularly the production of chemicals on which society now depends. The chemical process industries are heavily dependent on the availability of low-price petroleum as a feedstock. Recent life-cycle analyses suggest that pursuing both strategies of renewable energy sources and renewable feedstocks (i.e. biomass) will be required to meet these competing demands. Reducing the global use of both energy and manufactured chemicals will be a challenge for sustainable development. Education of the next generation of chemists and chemical engineers will have to change significantly from its current emphasis on petrochemical-based manufacturing to include a much greater emphasis on renewable resources and bio-based processes.Brief accounts of this work were presented at the 7th International Symposium on Green Chemistry in China (Zhuhai, People’s Republic of China, May 2005) and at the Joint US–China Green Chemistry Workshop (Beijing, People’s Republic of China, May 2005; this workshop was supported by US National Science Foundation grant CHE-0522369).     

The Antarctic Treaty System: Environmental protection,conservation, and the question of competing use

The Antarctic Treaty System consists of the Treaty itself, over 130 recommendations made under it, the Agreed Measures for the Conservation of Antarctic Fauna and Flora, the Convention for the Conservation of Antarctic Seals, and the Convention for the Conservation of Antarctic Marine Living Resources. Consultations have been held among parties to the Antarctic Treaty to elaborate an Antarctic minerals regime. It has become clear that how to deal with issues of competing use has begun to emerge as an important political question. In such a context the development of an Antarctic conservation strategy is a potentially helpful step. Competition of use, when it occurs, will be localised and different in different areas. In only tiny parts will it be severe, but these parts may be the biologically richest coastal areas. Various activities and their possible interactions are considered. It is concluded that any arrangement of Antarctic activities which given an automatic priority of one over others is wrong. Similarly, no activity should be subservient to all others. An Antarctic conservation strategy needs to be developed and in its operation the concept of adaptive environmental assessment and management needs to be applied. Within the Antarctic Treaty System there are moves towards assessment. What is needed now is a framework within which such concepts can operate; that is, a conservation and environmental strategy.     

The risks of risk-based regulation: insights from the environmental policy domain

Risk-based regulation has become increasingly popular in recent years. Proponents argue that it facilitates robust governance, contributing to efficient and effective use of regulatory resources and delivering interventions in proportion to risk. Critics contend that the challenges of operationalising risk-based governance mitigate its potential benefits. In this paper we start by considering what we mean by risk-based governance and discuss some of the factors shaping the adoption of such strategies. We then consider the development and operation of risk-based approaches in the environmental policy domain, focusing specifically on the regulation of contaminated land and radioactive waste. We argue that whilst risk-based approaches can offer important benefits, they face a range of epistemic, institutional and normative challenges that can play an important role in shaping the way that organisations manage both risks to society and their own institutional risks. This has profound implications for achieving regulatory objectives and, for this paper, the environmental outcomes that the regulations are designed to deliver.     

An extended input-output table for environmental and resources accounting

Environmentally Extended Input-Output(EEIO)tables have become a powerful element in supporting information-based environmental and economic policies.National-and provincial-level 10 tables are currently published by the National Bureau of Statistics of the People's Republic of China according to well-defined conventions.However,county-level 10tables are not provided as a rule by official statistics organizations.This paper conducts an overview of compiling EEIO tables for environmental and resources accounting at the county level and then answers several questions:First,what kind of data should be prepared for the compilation of county-level EEIO tables?Second,how can we set up comprehensive EEIO tables at the county level?Third,regarding the survey methods and the indirect modeling,which one should be chosen to build EEIO tables at the county level?Finally,what policy questions could such a table answer?EEIO tables at the county level can be used to predict the economic impacts of environmental policies and to perform trend and scenario analysis.     

Charismatic life: spectacular biodiversity and biophilic life writing

ABSTRACT

The essay uses the term “charismatic life” to describe representations of nature that emphasize vitality and vibrancy. Beginning with how life is reified when nature becomes spectacle, the essay discusses how a fetishism of life was part of the early structuring logic of biodiversity science in a way that undermined crafting other ethical and political responses to loss. When biodiversity emerged as a popular science concept in the 1980s, it was described as a scientific replacement for the sentimental attachment to charismatic megafauna that previously structured conservation priorities. But this essay argues, in a historicized reading of conservation biologist E.O. Wilson’s popular science memoir Biophilia [Wilson, E. O. (1984). Biophilia. Cambridge: Harvard University Press] alongside the seminal edited collection Biodiversity [Wilson, E. O. (Ed.). (1988). Biodiversity. Washington, DC: National Academy of Sciences], that Wilson’s sentimental biopolitics renders the world as if a collection of living souvenirs – tokens by which to remember forms of life that will have been lost.     

Management of risks in the chemical and nuclear areas

A comparative overiew is provided of some major aspects concerning assessment and management of chemical and nuclear risks arising as a consequence of accidents. Statutory procedures for constructing and running nuclear and chemical plants in Italy are discussed in detail. Special attention is given to the major changes that are likely to occur after the adoption of the EEC Council Directive 82/501, designed to prevent major accidents which might result from certain industrial activities and to limit their consequences for humans and their environment. Present status and future trends of accident analysis and risk assessment are also been dealt with, and special emphasis is placed on aspects common to both nuclear and chemical plants. Lastly, managerial aspects of contingency planning for, and response to, emergencies and accidents involving toxic chemical and/or ionizing radiations are examined with the aim of identifying more critical steps.     

Climate change risks in Sahelian Africa

Analyses of Sahel regional and country-specific rainfall and temperature time series derived from a fixed subset of stations show the well-documented large-scale decreasing trend in rainfall that occurred between 1970 and 2000 and also, an increasing trend in summertime maximum and wintertime minimum temperatures. The evolution of summertime mean maximum temperature is almost opposite to that of rainfall, and a significant correlation is observed between the evolution of this quantity and millet yields, in comparison with correlation with summertime rainfall. It appears that quantifying future vulnerability of the Sahel zone to climate change is rather difficult because climate models have not in general shown yet a satisfactory reproduction of the observed climate variability of this area.     

Health risks analysis of energy systems: Issues and approaches

Health risk analysis of energy systems is affected by various principles of law. In this paper those principles are discussed and linked to measures of risk, such as risk rates and the expected value, and to the cumulative distributions. These measures of risk are related to health decisionmaking, including case law. Uncertainty defeats decisionmaking, although such uncertainty is properly derived from scientific analyses. There is a paradox, in that portraying the uncertainty forestalls decisions. Yet at present, science cannot do better. Risk analysis is the tool to help resolve this problem by identifying irreducible uncertainty, that uncertainty which is present in most human activities.     

Climate and conflicts: the security risks of global warming

Since the publication of the fourth assessment report of the Intergovernmental Panel on Climate Change in 2007, the securitization of global warming has reached a new level. Numerous public statements and a growing research literature have discussed the potential security risks and conflicts associated with climate change. This article provides an overview of this debate and introduces an assessment framework of climate stress, human security and societal impacts. Key fields of conflict will be addressed, including water stress, land use and food security, natural disasters and environmental migration. A few regional hot spots of climate security will be discussed, such as land-use conflicts in Northern Africa; floods, sea-level rise and human security in Southern Asia; glacier melting and water insecurity in Central Asia and Latin America; water conflicts in the Middle East; climate security in the Mediterranean; and the potential impact on rich countries. Finally, concepts and strategies will be considered to minimize the security risks and move from conflict to cooperation in climate policy.     

Soil migration and plant uptake of technetium from a fluctuating water table

Soil columns (50x15 cm) were used to determine the potential for 95mTc (as a surrogate for 99Tc which is an important component of some radioactive waste) to migrate from a contaminated, fluctuating water table, through sandy loam soil and into perennial ryegrass. Upward migration was significantly retarded with, generally, only the bottom few centimetres of soil becoming contaminated over the 6 months of the experiment. This is thought to have been due to the presence of anoxic conditions within the water table leading to the reduction of pertechnetate to Tc(IV) species which are relatively insoluble. However, some evidence of very slow upward migration over time was found. Only a small and inconsistent transfer of activity into the perennial ryegrass was observed. Whilst these observations would suggest that 99Tc is less important than radionuclides such as 129I and 36Cl in terms of the risk associated with radioactive waste disposal, the potential for a slow upward migration, and/or a pulse-release following the re-oxidation of reduced soil in which 99Tc has accumulated should not be overlooked.     

Radioactive contamination in the Arctic--sources, dose assessment and potential risks

Arctic residents, whose diets comprise a large proportion of traditional terrestrial and freshwater foodstuffs, have received the highest radiation exposures to artificial radionuclides in the Arctic. Doses to members of both the average population and selected indigenous population groups in the Arctic depend on the rates of consumption of locally-derived terrestrial and freshwater foodstuffs, including reindeer/caribou meat, freshwater fish, goat cheese, berries, mushrooms and lamb. The vulnerability of arctic populations, especially indigenous peoples, to radiocaesium deposition is much greater than for temperate populations due to the importance of terrestrial, semi-natural exposure pathways where there is high radiocaesium transfer and a long ecological half-life for this radionuclide. In contrast, arctic residents with diets largely comprising marine foodstuffs have received comparatively low radiation exposures because of the lower levels of contamination of marine organisms. Using arctic-specific information, the predicted collective dose is five times higher than that estimated by UNSCEAR for temperate areas. The greatest threats to human health and the environment posed by human and industrial activities in the Arctic are associated with the potential for accidents in the civilian and military nuclear sectors. Of most concern are the consequences of potential accidents in nuclear power plant reactors, during the handling and storage of nuclear weapons, in the decommissioning of nuclear submarines and in the disposal of spent nuclear fuel from vessels. It is important to foster a close association between risk assessment and practical programmes for the purposes of improving monitoring, formulating response strategies and implementing action plans.     

Ways of improving the management of environmental risks

From the public's discovery of environmental quality in the late 1960s to the present, there has been increasing recognition that a more systematic approach is required to manage risks and to achieve the gains at low cost. Such a systematic approach must begin with risk identification, then go on to risk assessment, consideration of management options, a decision analysis of the options, and an examination of strategies for reducing loss. One of the most difficult aspects of environmental risk management is setting goals. There is a tendency to engage in rhetoric about zero risks and a pristine environment. However, moving toward more realistic goals requires consideration of what is an acceptable risk level. This level cannot be defined without knowing the benefits that come with the risk and the costs of reducing the risk. More generally, the criteria for selecting a risk management strategy include the residual level of risk, efficiency in reducing risk, equity, administrative simplicity, and public acceptability. A number of frameworks are currently used by U.S. regulatory agencies to manage risk: no-risk, risk-risk, technology-based standards, risk-benefit, cost-effectiveness, regulatory budget, and benefit-cost analysis. In specifying that an agency must use one of these frameworks, the U.S. Congress is implicitly specifying the goals for risk reduction. It appears to be easier for the U.S. Congress to specify a framework than a goal. Some of the nonregulatory means of managing risk include the market, and legal mechanisms. These risk management institutions have been effective and are a necessary part of any risk management program.     

Health risks of dietary exposure to perfluorinated compounds

Perfluorinated compounds (PFCs) form a diverse group of chemicals with surface-active properties manufactured for over 50 years. In recent years, a number of studies have reported the ubiquitous distribution of PFCs in human tissues and wildlife. Although the relative importance of the routes of human exposure to these compounds is not well established yet, it has been suggested that food intake and packaging, water, house dust, and airborne are all potentially significant sources. However, dietary intake is probably the main route of exposure to these compounds, including perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA), the most extensively investigated PFCs. This paper reviews the state of the science regarding the concentrations of PFCs in foodstuffs, human dietary exposure to these compounds and their health risks. The influence of processing, cooking and packaging on the PFCs levels in food is also discussed. Because of the rather limited information about human dietary exposure, studies to determine exposure to PFCs through the diet for the general population of a number of countries are clearly necessary. The correlation of PFCs body burdens and dietary intake of PFCs should be also established.