Bootstrap Estimation of Benchmark Doses and Confidence Limits with Clustered Quantal Data

The benchmark dose (BMD) is an exposure level that would induce a small risk increase (BMR level) above the background. The BMD approach to deriving a reference dose for risk assessment of noncancer effects is advantageous in that the estimate of BMD is not restricted to experimental doses and utilizes most available dose-response information. To quantify statistical uncertainty of a BMD estimate, we often calculate and report its lower confidence limit (i.e., BMDL), and may even consider it as a more conservative alternative to BMD itself. Computation of BMDL may involve normal confidence limits to BMD in conjunction with the delta method. Therefore, factors, such as small sample size and nonlinearity in model parameters, can affect the performance of the delta method BMDL, and alternative methods are useful. In this article, we propose a bootstrap method to estimate BMDL utilizing a scheme that consists of a resampling of residuals after model fitting and a one-step formula for parameter estimation. We illustrate the method with clustered binary data from developmental toxicity experiments. Our analysis shows that with moderately elevated dose-response data, the distribution of BMD estimator tends to be left-skewed and bootstrap BMDL s are smaller than the delta method BMDL s on average, hence quantifying risk more conservatively. Statistically, the bootstrap BMDL quantifies the uncertainty of the true BMD more honestly than the delta method BMDL as its coverage probability is closer to the nominal level than that of delta method BMDL. We find that BMD and BMDL estimates are generally insensitive to model choices provided that the models fit the data comparably well near the region of BMD. Our analysis also suggests that, in the presence of a significant and moderately strong dose-response relationship, the developmental toxicity experiments under the standard protocol support dose-response assessment at 5% BMR for BMD and 95% confidence level for BMDL.     

增算子不动点定理及其应用

本文建立了若干新的增算子不动点存在定理,作为应用,作者研究了在Banach空间中一类含间断项Volterra积分方程解的存在性,我们的结果改进和推广了诸多已知结果。     

英语教学与跨文化交际能力的培养

本文探讨了语言和文化的关系,并分析了我国英语教学的现状。文章指出文化教学是英语教学的重要组成部分。教师应该加强自身对文化教学意义的认识,努力提高学生对文化差异的敏感性,培养较强的跨文化交际能力,以适应时代发展的需要。     

提高体育专业学生英语学习能力的调查分析

对省内外七所高校不同体育专业学生英语学习能力的全面调查,发现体育专业学生英语能力与其心智发展特点有关;根据这种特点,采取相应的学法教法对策,使他们的英语学习能力得到迅速提高,并为特殊专业学生的英语教学提供了理论和实践依据。     

西部经济发展的生态学模式构建

面对世界经济绿化与软化发展趋势等四大背景,西部经济发展必须立足于生态学视野,实现以绿色产业为支柱、以知识经济为核心、以制度创新为突破口、以观念转变为动力,形成推动西部经济发展的生态学模式。     

九品中正制度再评价

九品中正制作为中国古代人才选拔制度发展的一个阶段 ,是察举制过渡到科举制的一个必经环节。它的发展演变来自两个方面的影响 ,一方面是为纠正察举制主观性太强的弊端而日益客观化的结果 ,另一方面 ,也是与当时各级官学和开馆授徒的私学全面衰落 ,而士族家学却一枝独秀状况相适应的。九品中正制在特定时期是起到了选拔优秀人才的作用的。     

经济学理性主义传统的当代流变

经济学的传统是以理性主义作为传统的,本文通过介绍经济学的发展,以一股新的理性主义、历史主义、系统思维或非理性主义的潮流,冲击主流经济学的理性主义传统,对经济学理论反思的同时,并对经济学的未来进行方法论的解读。     

对跨越资本主义卡夫丁峡谷理论的几点思考

19世纪后期,马克思恩格斯根据对俄国农村公社制度及俄国进入社会主义的道路问题进行深入的研究后提出了跨越资本主义卡夫丁峡谷的理论。我国学术界和理论界在讨论马克思主义的“跨越论”中,曾有人提出苏联和中国是“跨越论”的例证。我们认为,马克思主义关于跨越资本主义卡夫丁峡谷的理论是有着客观条件的,持“跨越论”观点的理论依据是不充分的。实际上,无论苏联还是中国都没有实现真正意义上的跨越。