Easy-to-construct confidence bands for comparing two simple linear regression lines

This paper shows how to construct confidence bands for the difference between two simple linear regression lines. These confidence bands provide directly the information on the magnitude of the difference between the regression lines over an interval of interest and, as a by-product, can be used as a formal test of the difference between the two regression lines. Various different shapes of confidence bands are illustrated, and particular attention is paid towards confidence bands whose construction only involves critical points from standard distributions so that they are consequently easy to construct.     

Eye-Tracking Data: New Insights on Response Order Effects and Other Cognitive Shortcuts in Survey Responding

Survey researchers since Cannell have worried that respondents may take various shortcuts to reduce the effort needed to complete a survey. The evidence for such shortcuts is often indirect. For instance, preferences for earlier versus later response options have been interpreted as evidence that respondents do not read beyond the first few options. This is really only a hypothesis, however, that is not supported by direct evidence regarding the allocation of respondent attention. In the current study, we used a new method to more directly observe what respondents do and do not look at by recording their eye movements while they answered questions in a Web survey. The eye-tracking data indicate that respondents do in fact spend more time looking at the first few options in a list of response options than those at the end of the list; this helps explain their tendency to select the options presented first regardless of their content. In addition, the eye-tracking data reveal that respondents are reluctant to invest effort in reading definitions of survey concepts that are only a mouse click away or paying attention to initially hidden response options. It is clear from the eye-tracking data that some respondents are more prone to these and other cognitive shortcuts than others, providing relatively direct evidence for what had been suspected based on more conventional measures.     

Planning in a state of turbulence

This paper is concerned with an exploration of the role of the long range planner, whether in the private or public sector of the economy, and the impact made upon the processes of his work by government's increasing propensity to manipulate the economy. The authors' researches over the last 2 years into the comparative nature of planning processes in the U.K. economy have made it abundantly clear to them that planners are increasingly concerned at the dangerous potential of such impact upon their forecasting procedures. The emphasis here will rest upon the planner in private enterprises, although the authors' work in both local government and the nationalized enterprises suggest that the problem is of equal importance in these sectors.The authors consider first the past nature of the search processes in long range planning and the context of such attempts to narrow down the range of variables that form the enterprise's perception of its future. Secondly, they examine the emerging discontinuity and the changing role of government, with particular reference to indicative planning concepts. Then they introduce some of the findings of a recent survey of attitudes towards long range planning in the construction industry of the U.K., a sector vitally influenced by turbulence in the economy and with particular interest in government's ideas of macro-planning. Finally Edwards and Harris examine the implications to government and to planners of their findings.     

Improvement of Highway Safety I: Identification of Causal Factors Through Fault-Tree Modeling1

As the first article of a two-part series, the purpose of this paper is to examine the functional factors that contribute to automobile accident occurrence and to model the causation structure in the form of a fault-tree. The fault-tree model provides an intuitive framework for qualitatively decomposing possible pathways to accident occurrence. Fault-tree analysis also provides a statistical representation of how interacting driver, vehicle, and environmental factors contribute to the likelihood of automobile accident occurrence. The application of this model facilitates pinpointing those factors that most contribute to accident causation and subsequently enables the identification and comparison of potential crash avoidance technologies.     

Pseudo Self-Consistent Estimation of a Copula Model with Informative Censoring

Abstract.  We consider the case where a terminal event censors a non-terminal event, but not vice versa. When the events are dependent, estimation of the distribution of the non-terminal event is a competing risks problem, while estimation of the distribution of the terminal event is not. The dependence structure of the event times is formulated with the gamma frailty copula on the upper wedge, with the marginal distributions unspecified. With a consistent estimator of the association parameter, pseudo self-consistency equations are derived and adapted to the semiparametric model. Existence, uniform consistency and weak convergence of the new estimator for the marginal distribution of the non-terminal event is established using theories of empirical processes, U -statistics and Z -estimation. The potential practical utility of the methodology is illustrated with simulated and real data sets.     

BAYESIAN HIDDEN MARKOV MODELS FOR LONGITUDINAL COUNTS

This paper describes a Bayesian approach to modelling carcinogenity in animal studies where the data consist of counts of the number of tumours present over time. It compares two autoregressive hidden Markov models. One of them models the transitions between three latent states: an inactive transient state, a multiplying state for increasing counts and a reducing state for decreasing counts. The second model introduces a fourth tied state to describe non‐zero observations that are neither increasing nor decreasing. Both these models can model the length of stay upon entry of a state. A discrete constant hazards waiting time distribution is used to model the time to onset of tumour growth. Our models describe between‐animal‐variability by a single hierarchy of random effects and the within‐animal variation by first‐order serial dependence. They can be extended to higher‐order serial dependence and multi‐level hierarchies. Analysis of data from animal experiments comparing the influence of two genes leads to conclusions that differ from those of Dunson (2000). The observed data likelihood defines an information criterion to assess the predictive properties of the three‐ and four‐state models. The deviance information criterion is appropriately defined for discrete parameters.     

精品课程建设中教材编写的创新思路探索——普通高等教育《土壤学》(“十五”国家级规划)教材的编写体会与实践

作者结合北京市精品课程建设,在组织编写普通高等教育“十五”国家级规划教材《土壤学》的过程中,认为首先应明确教材编写的指导思想,即在课程教材体系上有所创新,在课程教材内容上有所更新,在教学方法和手段上有所革新。同时在贯彻适用性和特色两个原则的基础上,进行了一些编写思路的探索和创新实践,这包括摸清读者底细、确定专业目标、把握课程内涵、了解市场需求,及正确处理好理论与应用、深度与广度、难度与易度、传统与创新、利教与利学、知识传授与技能培养的关系。通过以上步骤,保证了教材的先进性、系统性和特色,并实现了网络教学。     

提高理科基地生毕业论文质量的实践与思考

毕业论文是本科教育的重要环节,是实现本科人才培养目标的必由之路。近年来,由于受到诸多因素的影响,本科生毕业论文环节中暴露出许多问题,毕业论文的整体质量呈现下降的趋势。北京林业大学理科(生物学)基地通过几年的不断探索,在提高本科生毕业论文质量、培养创新人才方面积累了一定的经验,对促进和深化学校本科教育教学改革,提高本科人才培养质量具有积极的示范作用。     

Fertility Changes Among Immigrants: Generations,Neighborhoods, and Personal Characteristics*

Objective. To understand how adaptation/assimilation, disruption, and diffusion interact to produce changes in fertility levels among successive generations of Mexicans and Central Americans in the United States. Method. Using restricted access data that link individual data (CPS) to neighborhood data (census tracts), we examine the role of generation, personal characteristics, and neighborhood characteristics in determining children ever born (CEB). Results. There are significant differences in fertility across generations and, to a lesser extent, between women who live in ethnic enclaves and those who do not. Once personal characteristics are considered, the independent effect of generation on fertility is nearly eliminated. Personal characteristics dominate neighborhood characteristics in their ability to predict fertility. The most consistent predictor of CEB at the neighborhood level is the percentage of Hispanic adults. Conclusions. Personal characteristics dominate fertility change across generation, and were it not for increases in educational attainment, fertility might be higher in successive generations rather than lower or unchanged.     

Bayesian palaeoclimate reconstruction

Summary.  We consider the problem of reconstructing prehistoric climates by using fossil data that have been extracted from lake sediment cores. Such reconstructions promise to provide one of the few ways to validate modern models of climate change. A hierarchical Bayesian modelling approach is presented and its use, inversely, is demonstrated in a relatively small but statistically challenging exercise: the reconstruction of prehistoric climate at Glendalough in Ireland from fossil pollen. This computationally intensive method extends current approaches by explicitly modelling uncertainty and reconstructing entire climate histories. The statistical issues that are raised relate to the use of compositional data (pollen) with covariates (climate) which are available at many modern sites but are missing for the fossil data. The compositional data arise as mixtures and the missing covariates have a temporal structure. Novel aspects of the analysis include a spatial process model for compositional data, local modelling of lattice data, the use, as a prior, of a random walk with long-tailed increments, a two-stage implementation of the Markov chain Monte Carlo approach and a fast approximate procedure for cross-validation in inverse problems. We present some details, contrasting its reconstructions with those which have been generated by a method in use in the palaeoclimatology literature. We suggest that the method provides a basis for resolving important challenging issues in palaeoclimate research. We draw attention to several challenging statistical issues that need to be overcome.