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.     

新编《镇海县志》序言

镇海自五代始即已建县,在县治的一千余年中,她的地名曾数度更改,她的土地更是有沧海桑田之变化。近代以来随着社会历史的发展,镇海又有了天翻地覆的变化。如今,镇海县境虽析为宁波市治下的镇海区和北仑区,但这部新编的最后一部县志似可为镇海县千年历史的全面而真实的记载和总结。     

Going to Pieces: Paul Monette and the Fragments of the Tribe

Author of the highly acclaimed Borrowed Time: An AIDS Memoir (1988) and winner of the 1992 National Book Award for his autobiography Becoming a Man: Half a Life Story, Paul Monette died of complications from AIDS in Los Angeles on February 12, 1995. His most recent work, Last Watch of the Night: Essays Too Personal and Otherwise (1994), is his third volume in a trilogy of autobiographical writing on growing up gay, coming-out, and living with AIDS. A graduate of Phillips Academy and Yale University, Monette received a number of awards for his writing and his work as an outspoken voice in the battle against AIDS, including the National Book Award, three Lambda Literary awards, the PEN Center West Freedom to Write Award, and three honorary doctorate degrees, from Wesleyan University, the City University of New York, and the State University of New York at Oswego. A memorial service was held for Monette on Sunday, February 19, 1995, at the Directors Guild of America on Sunset Boulevard in Los Angeles. Paul Monette was 49.     

我国上市公司盈余管理行为的实证分析

我国证券市场存在较为严重的盈余管理现象.针对该现象,本文从盈余管理动机出发,分析我国上市公司盈余管理的行为特征.本文采用管理后盈余分布法,研究了我国上市公司2001年至2003年净资产收益率(ROE)的分布特征,发现我国上市公司仍然存在很强的盈余管理动机,而且我国上市公司盈余管理的行为受到政府监管的影响.最后,本文在实证研究的基础上提出了治理盈余管理的几点建议.     

学习策略的培养在外语多媒体教学中的必要性

课堂价值的核心在于培养学生主动学习、健康发展的意识和能力。一次为期两个学年的实证性教学实践证实:学习策略的培养在多媒体外语教学中是完全有必要性的,它不仅可以削减多媒体教学方式的负迁移,而且是实现课堂教学价值观的关键。     

民意调查在中国的发展和应用

民意调查在中国出现较早,但其发展还是始于党的十一届三中全会。1992年以后,中国的民意调查形成了调查主体、资金来源、调查内容多元化的发展态势,并且具有了新的发展特点。民意调查应用于社会的各个方面,主要表现在反映社会评价、辅助决策、社会监测、舆论沟通和学术促进等几个方面。     

Was there compression of disability for older Americans from 1992 to 2003?

Medical advances and the growth of the elderly population have focused interest on trends in the health of the elderly. Three theories have been advanced to describe these trends: compression of morbidity, expansion of morbidity, and dynamic equilibrium. We applied multistate life table methods to the Medicare Current Beneficiary Survey to estimate active and disabled life expectancy from 1992 to 2003, defining disability as having difficulty with instrumental activities of daily living or activities of daily living. We found increases in active life expectancy past age 65 and decreases in life expectancy with severe disability. These trends are consistent with elements of both the theory of compression of morbidity and the theory of dynamic equilibrium.     

Using age and spatial flow structures in the indirect estimation of migration streams

This article outlines a formal model-based approach for inferring interregional age-specific migration streams in settings where such data are incomplete, inadequate, or unavailable. The estimation approach relies heavily on log-linear models, using them to impose some of the regularities exhibited by past age and spatial structures or to combine and borrow information drawn from other sources. The approach is illustrated using data from the 1990 and 2000 U.S. and Mexico censuses.     

As low birth weight babies grow,can well-educated parents buffer this adverse factor? A research note

This research note combines two national Taiwanese data sets to investigate the relationships among low birth weight (LBW) babies, their parents' educational levels, and their future academic outcomes. We find that LBW is negatively correlated with the probability of such children attending college at age 18; however, when both parents are college or high school graduates, such negative effects may be partially offset. We also show that discrimination against daughters occurs, but only for daughters who were LBW babies. Moreover high parental education can buffer the LBW shock only among moderately LBW children (as compared with very LBW children) and full-term LBW children (as compared with preterm LBW children).     

Race,military service,and marital timing: Evidence from the NLSY-79

I use data from the 1979 National Longitudinal Study of Youth to examine the relationship between military service and marital timing for white men and black men during the 1980s. I use information about active-duty and reserve-duty service as well as veteran status to implement strong controls for selectivity. I find that active-duty military service increases the probability of first marriage for both whites and blacks. In part, this relationship is due to positive selectivity into the military and, for whites, to greater income and economic stability. Above and beyond the effects of selectivity, income, and economic stability, the effect of active-duty military service is particularly strong for black men.