What to Do at Low Doses: A Bounding Approach for Economic Analysis

To quantify the health benefits of environmental policies, economists generally require estimates of the reduced probability of illness or death. For policies that reduce exposure to carcinogenic substances, these estimates traditionally have been obtained through the linear extrapolation of experimental dose-response data to low-exposure scenarios as described in the U.S. Environmental Protection Agency's Guidelines for Carcinogen Risk Assessment (1986). In response to evolving scientific knowledge, EPA proposed revisions to the guidelines in 1996. Under the proposed revisions, dose-response relationships would not be estimated for carcinogens thought to exhibit nonlinear modes of action. Such a change in cancer-risk assessment methods and outputs will likely have serious consequences for how benefit-cost analyses of policies aimed at reducing cancer risks are conducted. Any tendency for reduced quantification of effects in environmental risk assessments, such as those contemplated in the revisions to EPA's cancer-risk assessment guidelines, impedes the ability of economic analysts to respond to increasing calls for benefit-cost analysis. This article examines the implications for benefit-cost analysis of carcinogenic exposures of the proposed changes to the 1986 Guidelines and proposes an approach for bounding dose-response relationships when no biologically based models are available. In spite of the more limited quantitative information provided in a carcinogen risk assessment under the proposed revisions to the guidelines, we argue that reasonable bounds on dose-response relationships can be estimated for low-level exposures to nonlinear carcinogens. This approach yields estimates of reduced illness for use in a benefit-cost analysis while incorporating evidence of nonlinearities in the dose-response relationship. As an illustration, the bounding approach is applied to the case of chloroform exposure.     

Dose-Response and Risk Assessment of Airborne Hexavalent Chromium and Lung Cancer Mortality

This study evaluates the dose-response relationship for inhalation exposure to hexavalent chromium [Cr(VI)] and lung cancer mortality for workers of a chromate production facility, and provides estimates of the carcinogenic potency. The data were analyzed using relative risk and additive risk dose-response models implemented with both Poisson and Cox regression. Potential confounding by birth cohort and smoking prevalence were also assessed. Lifetime cumulative exposure and highest monthly exposure were the dose metrics evaluated. The estimated lifetime additional risk of lung cancer mortality associated with 45 years of occupational exposure to 1 microg/m3 Cr(VI) (occupational exposure unit risk) was 0.00205 (90%CI: 0.00134, 0.00291) for the relative risk model and 0.00216 (90%CI: 0.00143, 0.00302) for the additive risk model assuming a linear dose response for cumulative exposure with a five-year lag. Extrapolating these findings to a continuous (e.g., environmental) exposure scenario yielded an environmental unit risk of 0.00978 (90%CI: 0.00640, 0.0138) for the relative risk model [e.g., a cancer slope factor of 34 (mg/kg-day)-1] and 0.0125 (90%CI: 0.00833, 0.0175) for the additive risk model. The relative risk model is preferred because it is more consistent with the expected trend for lung cancer risk with age. Based on statistical tests for exposure-related trend, there was no statistically significant increased lung cancer risk below lifetime cumulative occupational exposures of 1.0 mg-yr/m3, and no excess risk for workers whose highest average monthly exposure did not exceed the current Permissible Exposure Limit (52 microg/m3). It is acknowledged that this study had limited power to detect increases at these low exposure levels. These cancer potency estimates are comparable to those developed by U.S. regulatory agencies and should be useful for assessing the potential cancer hazard associated with inhaled Cr(VI).     

Benchmark Analysis: Shopping with Proper Confidence

We discuss the issue of using benchmark doses for quantifying (excess) risk associated with exposure to environmental hazards. The paradigm of low-dose risk estimation in dose-response modeling is used as the primary application scenario. Emphasis is placed on making simultaneous inferences on benchmark doses when data are in the form of proportions, although the concepts translate easily to other forms of outcome data.     

大学生心理问题及预防初探

当前 ,大学生心理问题不断出现 ,并由此引发了各种疾病 ,直接影响学生正常的学习和生活 ,为了帮助在校学生克服心理障碍 ,顺利完成学业 ,将来健康的走向社会、服务社会 ,作者建议各级教育管理部门及教育工作者 ,平时应重视学生出现的各种心理问题 ,用关心爱护、疏导等方式予以预防 ,只有这样 ,学生心理问题才能很好的得到解决 ,并愉快的投入到学习当中。     

试论资产评估折旧与会计折旧的区别

文章针对部分资产评估人员在建筑物折旧问题上存在的错误认识和做法 ,通过分析建筑物折旧的原因和重置成本法评估中折旧的实质 ,从多方面详细比较论述了资产评估折旧与会计折旧的区别     

理想点法综合评价学生数学成绩

应用多目标决策———理想点法 ,建立了一个综合评价学生数学成绩的数学模型     

Threshold decisions: how social workers prioritize referrals of child concern

This paper examines local authority social workers' decision‐making when considering referrals of children, where the concerns are on the margin of child protection procedures. In doing so, it describes the findings of a qualitative research study undertaken in the policy context of attempts to ‘refocus’ social work practice in the late 1990s and early twenty‐first century. Data collection involved interviews with social workers and parents in 23 cases. Conclusions are that referrals were evaluated on the basis of five key factors, specificity, severity, risk, parental accountability and corroboration, the use of which determined whether an initial assessment or an investigation of alleged abuse took place. The analysis builds on previous work in the child protection field, but demonstrates how the application of these factors differs between cases of child concern and cases of child protection. Policy implications concern the complexity of decision‐making in the uncertain context of limited referral information and it is proposed that the simplistic notion of a continuum of abuse is now outdated. Copyright © 2006 John Wiley & Sons, Ltd.     

Physiologically Based Liver Modeling and Risk Assessment

Because of the inherent complexity of biological systems, there is often a choice between a number of apparently equally applicable physiologically based models to describe uptake and metabolism processes in toxicology or risk assessment. These models may fit the particular data sets of interest equally well, but may give quite different parameter estimates or predictions under different (extrapolated) conditions. Such competing models can be discriminated by a number of methods, including potential refutation by means of strategic experiments, and their ability to suitably incorporate all relevant physiological processes. For illustration, three currently used models for steady-state hepatic elimination--the venous equilibration model, the parallel tube model, and the distributed sinusoidal perfusion model--are reviewed and compared with particular reference to their application in the area of risk assessment. The ability of each of the models to describe and incorporate such physiological processes as protein binding, precursor-metabolite relations and hepatic zones of elimination, capillary recruitment, capillary heterogeneity, and intrahepatic shunting is discussed. Differences between the models in hepatic parameter estimation, extrapolation to different conditions, and interspecies scaling are discussed, and criteria for choosing one model over the others are presented. In this case, the distributed model provides the most general framework for describing physiological processes taking place in the liver, and has so far not been experimentally refuted, as have the other two models. These simpler models may, however, provide useful bounds on parameter estimates and on extrapolations and risk assessments.     

人才测评及其功能和发展

人才测评的发展是经济建设和社会发展的必然要求 ,为此本文讨论了人才测评的功能、特性以及今后的发展方向 ,明确了人才测评在整体性人力资源开发和管理中的重要意义     

入世对我国旅游业的影响与对策研究

加入WTO对我国旅游业发展的总体影响是积极有利的.面对入世带来的各种影响,国内旅游企业(饭店、旅行社和旅游景区等)应更新观念,积极应变;与旅游业相关的政府主管部门应进行管理创新,为旅游业的全面发展创造良好的行业环境.