Estimating the variance in before-after studies

Problem

To simplify the computation of the variance in before-after studies, it is generally assumed that the observed crash data for each entity (or observation) are Poisson distributed. Given the characteristics of this distribution, the observed value (x_i) for each entity is implicitly made equal to its variance. However, the variance should be estimated using the conditional properties of this observed value (defined as a random variable), that is, f(x_i|μ_i), since the mean of the observed value is in fact unknown.

Method

Parametric and non-parametric bootstrap methods were investigated to evaluate the conditional assumption using simulated and observed data.

Results

The results of this study show that observed data should not be used as a substitute for the variance, even if the entities are assumed to be Poisson distributed. Consequently, the estimated variance for the parameters under study in traditional before-after studies is likely to be underestimated.

Conclusions

The proposed methods offer more accurate approaches for estimating the variance in before-after studies.     

基于物元模型的土地整理项目绩效评价方法与案例研究

随着新公共管理理念的普及和土地整理在我国社会经济发展中重要性的日益显著，对土地整理项目绩效评价理论、方法及实证研究意义重大。针对已有研究的不足，在界定土地整理项目绩效内涵基础上构建了基于“流程逻辑”框架的土地整理项目绩效评价指标体系，结合物元分析法建立了物元评价模型，并以浙江省永康市石柱镇土地整理项目为例，展开了实证研究。结果表明物元评价模型适合用于土地整理项目绩效评价。综合评价显示永康市石柱镇项目总体绩效水平为“较差”，绩效值为0.014 4。单指标评价显示:该项目只有4个指标绩效水平达到“良好及以上”，1个指标处于“一般”，其他的都处于“较差”水平；研究项目区的绩效水平主要受耕地面积增加率、土地利用提高率等9个因素影响。永康市在今后的土地整理项目建设中应该针对这些绩效影响因素采取相应措施，不断改善项目的整体绩效水平     

燃煤烟气低温SCR脱硝中试研究

低温选择性催化还原(SCR)脱硝是国内外脱硝技术研发的热点,但目前主要集中在实验室小试范围,无法完全反映催化剂在实际烟气中的运行状况。在30 t/h循环流化床燃煤锅炉脱硫除尘装置后建设了2 000~5 000 m3/h的SCR脱硝中试装置,经系统研究发现,中试使用的蜂窝式催化剂对SO2和NO具有很强的吸附能力,且反应温度、喷氨速率和气体空速均会影响催化脱硝效率。为期5 d的连续运行实验结果表明,催化剂的脱硝效率一直稳定在30%~50%,并未发现明显的失活,这证明设计除雾除尘器、较大的混合器、混合器与反应器间较长的管路均有利于缓解催化剂因SO2、H2O和飞灰中的碱性金属导致的失活。     

遥感监测土壤湿度综述

遥感技术具有大面积同步观测，时效性、经济性强等特点，为大面积动态监测土壤湿度提供了可能。本文对近年来国内外遥感监测土壤湿度的理论、方法的发展和应用进行了回顾，重点介绍了目前已经比较成熟和广泛应用的基于可见光与热红外波段的植被指数方法以及在干旱、半干旱地区的应用，通过对比分析了各种遥感监测方法的优缺点，指出了土壤湿度遥感监测方法存在的不足，展望了土壤湿度遥感监测方法的发展趋势。     

The environmental attitudes inventory: A valid and reliable measure to assess the structure of environmental attitudes

Environmental attitudes (EA), a crucial construct in environmental psychology, are a psychological tendency expressed by evaluating the natural environment with some degree of favour or disfavour. There are hundreds of EA measures available based on different conceptual and theoretical frameworks, and most researchers prefer to generate new measures rather than organize those already available. The present research provides a cumulative and theoretical approach to the measurement of EA, in which the multidimensional and hierarchical nature of EA is considered. Reported are findings from three studies on the development of a psychometrically sound, multidimensional inventory to assess EA cross-culturally, the Environmental Attitudes Inventory (EAI). The EAI has twelve specific scales that capture the main facets measured by previous research. The twelve factors were established through confirmatory factor analyses, and the EAI scales are shown to be unidimensional scales with high internal consistency, homogeneity and high test-retest reliability, and also to be largely free from social desirability.     

Stock market responses to chemical accidents in Japan: An event study

Despite recent major chemical process accidents in Japan, the top management teams of firms still avoid taking costly risk reduction measures because of their low perceived impact on firm performance. The disclosure of information on accident risks might motivate managers to enhance workplace safety because of the subsequent evaluation of firms by investors in stock markets. If the disclosed risk information is newly available for investors, firms with a high risk of accidents would receive a poor evaluation by stock markets and thus managers would take risk reduction measures to prevent stock prices from declining. In this study, we conduct an event study analysis to examine whether accident risk information is already reflected in stock prices, using data on the Japanese chemical industry. The results of our event study show that the estimated cumulative average abnormal returns of firms' stocks are significantly negative after severe accidents actually occurred. This finding implies that risk information is not already reflected in the stock prices of Japanese chemical firms and that the disclosure of accident risk information has the potential to motivate the top management teams of firms to reduce their firms’ accident risk.     

城市社会体育志愿者组织建设的实践性研究——以秦皇岛市社会体育志愿者组织为例

应用文献资料法、问卷调查法、实证研究法,探讨了城市社会体育志愿者组织建设的方法策略,即以高校社会体育专业成立志愿者分队为基点,依托当地已有的志愿者组织平台,融合吸纳更多的社会体育志愿者加入社会体育志愿者大队。通过社会体育志愿者分队的组建及服务项目的实施,为政府落实《建立全民健身志愿服务长效化机制工作方案》提供参考意见,同时也为提高社会体育专业学生的专业能力和人文素养搭建平台。     

湖南2008/2011年两次低温雨雪冰冻灾害成因与影响对比分析

针对2008年1月13日-2月2日和2011年1月1-23日两次低温雨雪冰冻过程,从天气学成因、对交通、电力影响情况和特点等方面进行综合对比分析,揭示了两次过程的强度和造成灾情差异的原因,并提出了如何进一步防御和减轻极端天气气候事件灾害的能力,为暴雪冰冻灾害防御提供经验和依据。     

Citizen science networks in natural history and the collective validation of biodiversity data

Biodiversity data are in increasing demand to inform policy and management. A substantial portion of these data is generated in citizen science networks. To ensure the quality of biodiversity data, standards and criteria for validation have been put in place. We used interviews and document analysis from the United Kingdom and The Netherlands to examine how data validation serves as a point of connection between the diverse people and practices in natural history citizen science networks. We found that rather than a unidirectional imposition of standards, validation was performed collectively. Specifically, it was enacted in ongoing circulations of biodiversity records between recorders and validators as they jointly negotiated the biodiversity that was observed and the validity of the records. These collective validation practices contributed to the citizen science character or natural history networks and tied these networks together. However, when biodiversity records were included in biodiversity‐information initiatives on different policy levels and scales, the circulation of records diminished. These initiatives took on a more extractive mode of data use. Validation ceased to be collective with important consequences for the natural history networks involved and citizen science more generally.     

农业生态与土地退化的土壤微形态研究

简要地介绍了土壤微形态研究方法及其在农业生态与土地退化研究中的应用,并回顾了近20a的国际土壤微形态研究的内容与进展.在过去的20a中,土壤微形态学在概念、现象的解释、分析技术'以及应用上都取得了前所未有的进展.特别在样品脱水方法、荧光分析、图象处理及定量分析技术上得到很大的发展.植物根系与土壤微结构的关系,土壤改良对结构的影响等方面研究取得一定的成就.利用土壤微形态研究农业生态系统中的根系与根际的生态过程,作物对水分和养分的吸收过程,人为活动对土壤退化,熟化的微形态指标,以及利用微形态指标评价人为因素在现代土壤过程中的作用等,是土壤微形态研究的最新动态.