bluuebunny/crossref_metadata_2025 huggingface dataset:
Improving the Elevation Accuracy of Digital Elevation Models: A Comparison of Some Error Detection Procedures
Authors: López Carlos
Published: March 2003

The widespread availability of powerful desktop computers, easy‐to‐use software tools and geographic datasets have raised the quality problem of input data to be a crucial one. Even though accuracy has been a concern in every serious application, there are no general tools for its improvement. Some particular ones exist, however, and some results are presented here for a particular case of quantitative raster data: Digital Elevation Models (DEM). Two procedures designed to detect anomalous values (also named gross errors, outliers or blunders) in DEMs, but valid also for other quantitative raster datasets, were tested. A DEM with elevations varying from 181 to 1044 m derived from SPOT data has been used as a contaminated sample, while a manually derived DEM obtained from aerial photogrammetry was regarded as the ground truth to allow a direct performance comparison for the methods with real errors. It is assumed that a “better” value can be measured or obtained through some methodology once an outlier location is suggested. The options are different depending upon the user (DEM producers might go to the original data and make another reading, while end users might use interpolation). Both choices were considered in this experiment. Preliminary results show that for the available dataset, the accuracy might be improved to some extent with very little effort. Effort is defined here as the percentage of points suggested by the methodology in relation with its total number: thus 100 per cent effort implies that all points have been checked. The method proposed by López (1997) gave poor results, because it has been designed for errors with low spatial autocorrelation (which is not the case here). A modified version was then designed and compared with the method proposed by Felicísimo (1994). The three procedures can be applied both for error detection during DEM generation and by end users, and they might be of use for other quantitative raster data. The choice of the best methodology is different depending on the effort involved. The conclusions have been derived for a photogrammetrically obtained DEM; other production procedures might lead to different results.
Fuzzy Set Approaches to Spatial Data Mining of Association Rules
Authors: Ladner R , Petry F E , Cobb M A
Published: March 2003

This paper presents an approach to the discovery of association rules for fuzzy spatial data. Association rules provide information of value in assessing significant correlations that can be found in large databases. Here we are interested in correlations of spatially related data such as soil types, directional or geometric relationships, etc. We have combined and extended techniques developed in both spatial and fuzzy data mining in order to deal with the uncertainty found in typical spatial data.
Synonymy blocking and the elsewhere condition: lexical morphology and the speaker
Authors: Giegerich Heinz J.
Published: March 2003

This article investigates the extent to which synonymy blocking occurs in the synchronic derivation and, more controversially, whether it is predicted by the Elsewhere Condition (EC). It argues that in current Lexical Morphology, EC accurately predicts the presence of ‘token blocking’ and the absence of ‘type blocking’, that apparent token‐blocking failure is due either to non‐synonymy or to overregularization, and that apparent type‐blocking is due to an informal tendency of synonymy avoidance rather than to EC. A revised version of EC is proposed which brings to light a number of patterns in the behaviour of ‘rival’ processes including the Strict Cyclicity Effect in phonology.
Capital Flight from Russia
Authors: Loungani Prakash , Mauro Paolo
Published: March 2003

This paper documents the scale of capital flight from Russia, compares it with that observed in other countries, and reviews policy options. The evidence from other countries suggests that capital flight can be reversed once reforms take hold. The paper argues that capital flight from Russia can only be curbed through a medium‐term reform strategy aimed at improving governance and macroeconomic performance, and strengthening the banking system. Capital controls result in costly distortions and should gradually be phased out as part of that medium‐term strategy.
Ideologies of English in Japan
Authors: Kubota Ryuko
Published: March 2003

A number of educators in recent years have argued that the dominance of English has created structural and cultural inequalities between developed and developing countries. Although they tend to dismiss ideological issues regarding teaching English in affluent countries in the Expanding Circle such as Japan, there is a growing concern and critique in Japan on ideologies of English. Critics argue that the dominance of English influences the Japanese language and people’s views of language, culture, race, ethnicity and identity which are affected by the world view of native English speakers, and that teaching English creates cultural and linguistic stereotypes not only of English but also of Japanese people. Recent discourses of nihonjinron and kokusaika provide a broader context for understanding such ideologies. These discourses represent both resistance and accommodation to the hegemony of the West with a promotion of nationalistic values and learning a Western mode of communication; i.e., English. Among several proposals offered by critics, raising critical awareness of English domination parallels the philosophy of critical pedagogy. This paper suggests that both critical consciousness and practical skills in English along with inclusion of varieties of English in the curriculum are necessary for Japanese learners to appropriate English for social transformation.
Nativization in Brunei English: Deviation vs. Standard
Authors: Svalberg Agneta M.‐L.
Published: March 2003

It has been argued that a non‐standard variety of English, Brunei English (BNE) is being spoken in Brunei (Cane, 1993). In the following paper it is suggested that BNE is still at an early stage of development and that there is still little awareness among its speakers of some of the differences between it and Standard British English (STE) but that BNE is likely to expand and stabilize. A Grammaticality Judgement test was administered to 106 first‐year students at Universiti Brunei Darussalam in an attempt to find non‐standard uses of English verb forms which were acceptable to subjects regardless of proficiency level. It was hypothesized that such uses would form part of the BNE repertoire. Three exponents which might be assigned this status were identified, two of which were subsequently found to be frequent in public texts. The paper explores the possible meanings in BNE of these non‐standard uses and argues that they serve an expressive need of BNE speakers. It is suggested that certain STE uses might even have become socially inappropriate in a Bruneian context
Intelligibility and Comprehensibility of American andIrish Englishes in Japan
Authors: Matsuura Hiroko , Chiba Reiko , Fujieda Miho
Published: March 2003

The present study focuses on the effect of familiarity with different English accents. Specifically, the study investigates Japanese university students’ intelligibility and comprehensibility judgements of familiar and unfamiliar English – American English and Irish English, respectively. To see to what extent each variety was intelligible to them, subjects were asked to listen to self introductions of native speakers and fill missing words in blanks. To examine how comprehensible the varieties were, they were asked to indicate their judgements subjectively by using 7‐point scales. Findings include: (1) Even if the listeners felt an utterance was easy to understand, it did not necessarily mean they could transcribe the words or understand the message correctly; (2) the amount of exposure and familiarity seemed to be factors contributing to higher perceived comprehensibility but not necessarily to better understanding of the message; and (3) listeners’ perception of speech was likely to be affected by salient vocal features such as clarity, intonation, fluency and pauses. It is assumed that familiarity and exposure had at least a positive psychological effect on the listeners, which could lead to less inhibition, bias toward and more tolerance of different varieties of English.
Double Standards: Teacher Education in the Expanding Circle
Authors: Seidlhofer Barbara
Published: March 2003

This paper describes some of the dilemmas which non‐native teachers of English worldwide face as they are exposed to the competing discourses of educational ideologies and market forces and have to somehow reconcile the contradictory demands of global claims and pressures with the local conditions in which they work. It is argued that it is vital to resist a simple transfer of teaching approaches and attitudes originating from the Inner Circle to the Expanding Circle, where quite different conditions obtain. The status and role of non‐native speaker teachers is explored in this paper, drawing on an empirical study of the self‐perception of Austrian teachers, and suggestions are made as to how teachers can take advantage of their non‐native speaker status and develop it as an important resource for asserting the needs and preferences of their specific Expanding Circle settings. Teacher education plays a crucial role in making teachers aware of their non‐native assets and in preparing them explicitly to exploit these assets in the development of an appropriate pedagogy.
Issues in Reconstructing Earlier African‐American English
Authors: Wolfram Walt
Published: March 2003

Despite intense scrutiny over the past several decades, there remain a number of unresolved issues in the reconstruction of the historical development of African‐American Vernacular English (AAVE). These issues concern the reliability of written texts representing earlier AAVE, the representativeness of the spoken data from ex‐slave recordings and remnant transplant communities, the delimitation of the sociohistorical context of earlier AAVE development, the nature of inter‐ and intra‐community variation in earlier AAVE, and the principles for identifying donor sources for AAVE structures. Evidence from representative written sources is compared, along with spoken language data from a long‐term, bi‐racial remnant community in coastal North Carolina. The spoken language data demonstrate that earlier AAVE was affected both by its original contact history and the localized varieties spoken by European American cohort communities. Furthermore, data indicate that there was considerable intra‐community as well as inter‐community language variation among earlier African Americans. The analysis shows that sociolinguists need to reconstruct the historical development of AAVE in a way that is consistent with the sociohistorical and demographic circumstances of early African Americans; faithful to an understanding of contact linguistics, independent language development, and dialect diffusion; and sensitive to the local sociolinguistic situations that have contextualized different groups of individual African Americans within these communities.
Creative destruction: Singapore’s Speak Good English movement
Authors: Rubdy Rani
Published: March 2003

The increasing use of Singlish in the media, in early schooling and other everyday domains reflects its growing importance as a symbol of social identity and cohesion in Singapore. However, this trend runs counter to the country’s avowed economical goals of becoming a knowledge hub in the region, which it seeks to achieve by developing a highly skilled service sector that is proficient in (Standard) English. Thus, paradoxically, despite a new policy initiative to loosen their traditional tight grip on society in the interest of developing a nation of creative risk‐takers, the authorities have recently launched the Speak Good English movement, spawning a slew of editorials, cartoons, skits and commercials in a vigorous attempt at generating awareness among the public of the need to promote the use of Standard English. This paper attempts to show that this move to stem the popularity of Singlish is yet another manifestation of the notion of “creative destruction,” currently being proposed as a strategy to improve the efficiency of corporate and industrial businesses in the country. “Creative destruction” entails the partial destruction of existing economic ideas and structures which rapidly obsolesce with the emergence of new ones. Drawing a parallel with the Speak Mandarin campaign, which has successfully resulted in the dispersal of the local Chinese dialects, the paper argues that this attempt to replace Singlish by Standard English, while throwing up valid issues of social identity and cohesiveness, which are prone to get subsumed by the more urgent pragmatic and economic rationalizations proffered, can then be seen as a triumph of the relentless, hegemonic forces of globalization.
Evolutionary Ethics: Its Origin and Contemporary Face
Authors: Thompson Paul
Published: March 2003

The development of modern evolutionary ethics began shortly after the publication of Charles Darwin's On the Origin of Species by Natural Selection. Early discussions were plagued by several problems. First, evolutionary ethical explanations were dependent on group‐selection accounts of social behavior (especially the explanation of altruism). Second, they seem to violate the philosophical principle that “ought” statements cannot be derived from “is” statements alone (values cannot be derivedfrom facts alone). Third, evolutionary ethics appeared to be biologically deterministic, deemed incompatible with the free will required for ethics to be possible. Fourth, social policies based on evolutionary theory (for example, eugenics in the early part of this century) seemed patently unethical. Sociobiology (which coalesced as a field of study with Edward O. Wilson's Sociobiology: The New Synthesis, 1975) addressed several of these problems and provided a rich framework and a new impetus for evolutionary ethics. The lingering problems were the philosophical is‐ought barrier and biological determinism. After tracing the early and more recent development of evolutionary ethics, I argue that the remaining problems can be surmounted and an incipient evolutionary ethics can be defended. Thoroughgoing evolutionaryethics must await theoretical developments in neurobiology and cognitive science.
Dealing with Extremists in Public Discussion: Front National and ‘Republican Front’ in France
Authors: Fennema Meindert , Maussen Marcel
Published: March 2003

In this article we investigate the way modern democracies can deal with extremists in public discussion. The first part of the article conceptualizes political discussion insofar as it makes a contribution to the democratic process. We focus upon the democratic process as a way of dealing with conflicts between citizens that stem from differences in moral outlook. We reflect upon this process mainly in relation to its capacity to overcome possible political deadlocks, in the perspective of collective decision making. In the second part we concentrate on the question of how public discussion in a modern democracy should look. Here, then, we take a similar perspective as Gutmann and Thompson (1996) in saying that we should try and define some central ‘rules of the game’ for public discussion. We make a distinction between entrance rules that are proscriptive and performative rules that are suggestive.
Free Riding on Altruism and Group Size
Authors: Hindriks Jean , Pancs Romans
Published: March 2003

It is shown that altruism does not affect the equilibrium provision of public goods although altruism takes the form of unconditional commitment to contribute. The reason is that altruistic contributions completely crowd out selfish voluntary contributions. That is, egoists free ride on altruism. It is also shown that public goods are less likely to be provided in larger groups. The only qualification to our results is when the probability of altruism is so high that it is a dominant strategy for all egoistic players to free ride. In this case, actually, both altruism and the larger group facilitate public good provision.
Urbanization Patterns: European Versus Less Developed Countries
Authors: Puga Diego
Published: March 2003

This paper develops a model in which the interaction between transport costs, increasing returns to scale, and labor migration across sectors and regions creates a tendency for urban agglomeration. Demand from rural areas favors urban dispersion. European urbanization took place mainly in the 19th century, with higher costs of spatial interaction, weaker economies of scale, and a less‐elastic supply of labor to the urban sector than in less developed countries (LDCs) today. These factors could help explain why primate cities dominate in LDCs, whereas a comparatively small share of urban population lives in Europe's largest cities.
Environmental Compliance Costs and the Distribution of Emissions in the U.S.
Authors: Millimet David L. , Slottje Daniel
Published: March 2003

Using the properties of the Gini coefficient, a structural model is developed to assess the impact of uniform changes in environmental compliance costs on the distribution of per capita emissions across U.S. counties and states, a distribution that places a larger burden on minorities. Using data from the U.S. EPA’s Toxic Release Inventory and three state‐specific measures of environmental compliance costs, we find that uniform increases in federal environmental standards have little impact on the distribution of environmental hazards, and may actually exacerbate spatial inequality. As a result, Federal standards that target specific high pollution locations are necessary to redress current inequities.
The District and the Global Economy: Exportation Versus Foreign Location
Authors: Basevi Giorgio , Ottaviano Gianmarco I.P.
Published: March 2003

We depict an industrial district as a center of innovation where positive local spillovers sustain the endogenous invention of new goods by profit‐seeking firms. After invention, firms face a crucial choice between reaching distant markets by export or plant delocation. Attempts by firms to circumvent trade barriers through delocation slow down the pace of innovation and harm the welfare of the district.
The Dharma of Ethics, the Ethics of Dharma: Quizzing the Ideals of Hinduism
Authors: Dhand Arti
Published: March 2003

This paper is divided into six parts. The first presents a rudimentary definition of ethics based on Western philosophical theories, particularly their concern for articulating universal moral principles. The second examines the assumptions anchoring Western moral philosophies, and raises the question: are the philosophical presuppositions of modern Western philosophy consistent with the presuppositions of Hinduism? It concludes that the two are not entirely in agreement, particularly on the issue of personal and social identity. The third section locates areas in Hinduism that discursively concur with the concerns of Western ethicists, and explores the limits of the semblance. The fourth identifies problematic areas, and raises the question: should the idea of universal ethics be abandoned for Hinduism? The fifth section concludes that such abandonment would be hasty, and initiates a searching look into the Hindu epics for concepts that, while not identical with may still be parallel to some Western notions of ethics. The sixth looks at the content of normative Hindu morality, and generalizes on the basis of this content about the nature of “Hindu ethics”.
Fierce Words: Repositionings of Caste and Devotion in Traditional Śrvaisnava Hindu Ethics
Authors: Clooney Francis X.
Published: March 2003

In the 13th and 14th centuries CE the Śrvaisnava Hindu community of south India struggled to integrate the traditional values of the older brahmanical hierarchical system with the devotional egalitarianism that had come to the fore with fresh force in the Tamil vernacular tradition in the 7th and 8th centuries and thereafter. One of the most vexed aspects of this integration pertained to caste, and whether devotionalism foreclosed a continuation of traditional caste distinctions: do divine love and grace mandate radical egalitarianism? Śrvaisnava theologians were divided on the issue, some more conservative, some more radical in their rhetoric about continuity and change. Yet, as this essay argues, none were willing to go to the extremes either of dismissing caste structures entirely or of entirely subordinating devotion to caste. New values were to take primary place, while old norms were to be reinterpreted and given new meanings. Analyzing well–known examples from the tradition they argued instead a balance between norms and exceptions, treating violations of caste as occasions to glorify the power of devotion but without predicting the end of caste altogether. Attention to this case sheds light on caste and devotion in the Hindu context, the nature of ethical debate in India, and consequently too ways in which rhetoric functions more widely in ethical analysis.
Taking Sin Seriously
Authors: Weaver Darlene Fozard
Published: March 2003

Contemporary Roman Catholic ethics endeavors to take sin seriously by offering theologies of sin that emphasize it as a force and as a basic, personal orientation. Such efforts rightly counter the Catholic tradition's earlier reduction of sin to sins, and sins to external acts and moral culpability. But perhaps they go too far in this regard. By engaging Charles Curran, this study argues that inattention to sins undermines the theological referent of sin as a discourse that concerns more than moral culpability, obscures God as the source of freedom and value, and neglects the way in which acts express and sustain sin and fashion a personal orientation. Drawing on the work of Jean Porter, the essay shows that attention to sins highlights the historicity, particularity, and provisionality of human acts because of the theological referent and analogical character of sin and sins.
Learning about literacy: Children’s versions of the Literacy Hour
Authors: Hanke Veronica
Published: March 2003

This article reports on an enquiry into the responses of a class of Year 1 children, aged 5‐6 years, to the first eight months of the National Literacy Strategy (NLS). Children were given incomplete drawings to represent the four parts of the Literacy Hour. In completing the drawings the children made their own interpretations of the Literacy Hour. They could choose to write thought or speech bubbles, draw faces and expressions, make written or dictated comments about the teacher and the children portrayed. The methodology enabled these young children to articulate detailed responses to their experience of a particular style of teaching. Each child documented a range of attitudes to and feelings about whole class teaching, group work and the plenary session. These insights, which were often challenging, put the emotional dimension of learning at the centre of their experiences of the NLS.
Does Social Mobility Affect the Size of the Socioeconomic Mortality Differential?: Evidence from the Office for National Statistics Longitudinal Study
Authors: Blane D. , Harding S. , Rosato M.
Published: March 2003

The effect of social mobility on the socioeconomic differential in mortality is examined with data from the Office for National Statistics Longitudinal Study. The analyses involve 46 980 men aged 45–64 years in 1981. The mortality risk of the socially mobile is compared with the mortality risk of the socially stable after adjustment for their class of origin (their social class in 1971) and class of destination (their social class in 1981) separately. Among those in employment there is some evidence that movement out of their class of origin is in the direction predicted by the idea of health-related social mobility. This evidence, however, seems strongest for causes of death which are least likely to have been preceded by prolonged incapacity. Movement into the class of destination, however, shows the opposite relationship with mortality. Compared with the socially stable members of their class of destination, the upwardly mobile tend to have higher mortality and the downwardly mobile tend to have lower mortality. This relationship with the class of destination, it is suggested, may explain why socioeconomic mortality differentials do not widen with increasing age.
Multivariate Multilevel Analyses of Examination Results
Authors: Yang Min , Goldstein Harvey , Browne William , Woodhouse Geoffrey
Published: March 2003

In the study of examination results much interest centres on comparisons of curriculum subjects entered and the correlation between these at individual and institution level based on data where not every individual takes all subjects. Such ‘missing’ data are not missing at random because individuals deliberately select subjects that they wish to study according to criteria that will be associated with their performance. In this paper we propose multivariate multilevel models for the analysis of such data, adjusting for such subject selection effects as well as for prior achievement. This then enables more appropriate institutional comparisons and correlation estimates. We analyse A- and AS-level results in different mathematics papers of 52 587 students from 2592 institutions in England in 1997. Although this paper is concerned largely with methodology, substantive findings emerge on the effects of gender, age, intakes of General Certificate of Education pupils, examination board and establishment type for A- and AS-level mathematics.
Semiparametric Bayesian Inference for Time Series with Mixed Spectra
Authors: Carter C. K. , Kohn R.
Published: March 2003

A Bayesian analysis is presented of a time series which is the sum of a stationary component with a smooth spectral density and a deterministic component consisting of a linear combination of a trend and periodic terms. The periodic terms may have known or unknown frequencies. The advantage of our approach is that different features of the data—such as the regression parameters, the spectral density, unknown frequencies and missing observations—are combined in a hierarchical Bayesian framework and estimated simultaneously. A Bayesian test to detect deterministic components in the data is also constructed. By using an asymptotic approximation to the likelihood, the computation is carried out efficiently using the Markov chain Monte Carlo method in O(Mn) operations, where nis the sample size and Mis the number of iterations. We show empirically that our approach works well on real and simulated samples.
The EM Algorithm—an Old Folk-song Sung to a Fast New Tune
Authors: Meng Xiao-Li , Van Dyk David
Published: March 2003

Celebrating the 20th anniversary of the presentation of the paper by Dempster, Laird and Rubin which popularized the EM algorithm, we investigate, after a brief historical account, strategies that aim to make the EM algorithm converge faster while maintaining its simplicity and stability (e.g. automatic monotone convergence in likelihood). First we introduce the idea of a ‘working parameter’ to facilitate the search for efficient data augmentation schemes and thus fast EM implementations. Second, summarizing various recent extensions of the EM algorithm, we formulate a general alternating expectation–conditional maximization algorithm AECM that couples flexible data augmentation schemes with model reduction schemes to achieve efficient computations. We illustrate these methods using multivariate t-models with known or unknown degrees of freedom and Poisson models for image reconstruction. We show, through both empirical and theoretical evidence, the potential for a dramatic reduction in computational time with little increase in human effort. We also discuss the intrinsic connection between EM-type algorithms and the Gibbs sampler, and the possibility of using the techniques presented here to speed up the latter. The main conclusion of the paper is that, with the help of statistical considerations, it is possible to construct algorithms that are simple, stable and fast.
Some Properties and Generalizations of Non-negative Bayesian Time Series Models
Authors: Grunwald Gary K. , Hamza Kais , Hyndman Rob J.
Published: March 2003

We study the most basic Bayesian forecasting model for exponential family time series, the power steady model (PSM) of Smith, in terms of observable properties of one-step forecast distributions and sample paths. The PSM implies a constraint between location and spread of the forecast distribution. Including a scale parameter in the models does not always give an exact solution free of this problem, but it does suggest how to define related models free of the constraint. We define such a class of models which contains the PSM. We concentrate on the case where observations are non-negative. Probability theory and simulation show that under very mild conditions almost all sample paths of these models converge to some constant, making them unsuitable for modelling in many situations. The results apply more generally to non-negative models defined in terms of exponentially weighted moving averages. We use these and related results to motivate, define and apply very simple models based on directly specifying the forecast distributions.
Balanced Confidence Regions Based on Tukey’s Depth and the Bootstrap
Authors: Yeh Arthur B. , Singh Kesar
Published: March 2003

We propose and study the bootstrap confidence regions for multivariate parameters based on Tukey’s depth. The bootstrap is based on the normalized or Studentized statistic formed from an independent and identically distributed random sample obtained from some unknown distribution in R  q. The bootstrap points are deleted on the basis of Tukey’s depth until the desired confidence level is reached. The proposed confidence regions are shown to be second order balanced in the context discussed by Beran. We also study the asymptotic consistency of Tukey’s depth-based bootstrap confidence regions. The applicability of the method proposed is demonstrated in a simulation study.
Weighting for Unequal Selection Probabilities in Multilevel Models
Authors: Pfeffermann D. , Skinner C. J. , Holmes D. J. , Goldstein H. , Rasbash J.
Published: March 2003

When multilevel models are estimated from survey data derived using multistage sampling, unequal selection probabilities at any stage of sampling may induce bias in standard estimators, unless the sources of the unequal probabilities are fully controlled for in the covariates. This paper proposes alternative ways of weighting the estimation of a two-level model by using the reciprocals of the selection probabilities at each stage of sampling. Consistent estimators are obtained when both the sample number of level 2 units and the sample number of level 1 units within sampled level 2 units increase. Scaling of the weights is proposed to improve the properties of the estimators and to simplify computation. Variance estimators are also proposed. In a limited simulation study the scaled weighted estimators are found to perform well, although non-negligible bias starts to arise for informative designs when the sample number of level 1 units becomes small. The variance estimators perform extremely well. The procedures are illustrated using data from the survey of psychiatric morbidity.
Model-based Inference for Categorical Survey Data Subject to Non-ignorable Non-response
Authors: Forster Jonathan J. , Smith Peter W. F.
Published: March 2003

We consider non-response models for a single categorical response with categorical covariates whose values are always observed. We present Bayesian methods for ignorable models and a particular non-ignorable model, and we argue that standard methods of model comparison are inappropriate for comparing ignorable and non-ignorable models. Uncertainty about ignorability of non-response is incorporated by introducing parameters describing the extent of non-ignorability into a pattern mixture specification and integrating over the prior uncertainty associated with these parameters. Our approach is illustrated using polling data from the 1992 British general election panel survey. We suggest sample size adjustments for surveys when non-ignorable non-response is expected.
An Optimization Interpretation of Integration and Back-Fitting Estimators for Separable Nonparametric Models
Authors: Nielsen J. P. , Linton O. B.
Published: March 2003

We provide an optimization interpretation of both back-fitting and integration estimators for additive nonparametric regression. We find that the integration estimator is a projection with respect to a product measure. We also provide further understanding of the back-fitting method.
Test Inversion Bootstrap Confidence Intervals
Authors: Carpenter James
Published: March 2003

In this paper we explore the theoretical and practical implications of using bootstrap test inversion to construct confidence intervals. In the presence of nuisance parameters, we show that the coverage error of such intervals is O(n  −1/2) which may be reduced to O(n  −1) if a Studentized statistic is used. We present three simulation studies and compare the performance of test inversion methods with established methods on the problem of estimating a confidence interval for the dose–response parameter in models of the Japanese atomic bomb survivors data.
Bayesian Latent Variable Models for Clustered Mixed Outcomes
Authors: Dunson David B.
Published: March 2003

A general framework is proposed for modelling clustered mixed outcomes. A mixture of generalized linear models is used to describe the joint distribution of a set of underlying variables, and an arbitrary function relates the underlying variables to be observed outcomes. The model accommodates multilevel data structures, general covariate effects and distinct link functions and error distributions for each underlying variable. Within the framework proposed, novel models are developed for clustered multiple binary, unordered categorical and joint discrete and continuous outcomes. A Markov chain Monte Carlo sampling algorithm is described for estimating the posterior distributions of the parameters and latent variables. Because of the flexibility of the modelling framework and estimation procedure, extensions to ordered categorical outcomes and more complex data structures are straightforward. The methods are illustrated by using data from a reproductive toxicity study.
On Heteroscedastic Hazards Regression Models: Theory and Application
Authors: Hsieh Fushing
Published: March 2003

A class of non-proportional hazards regression models is considered to have hazard specifications consisting of a power form of cross-effects on the base-line hazard function. The primary goal of these models is to deal with settings in which heterogeneous distribution shapes of survival times may be present in populations characterized by some observable covariates. Although effects of such heterogeneity can be explicitly seen through crossing cumulative hazards phenomena in k-sample problems, they are barely visible in a one-sample regression setting. Hence, heterogeneity of this kind may not be noticed and, more importantly, may result in severely misleading inference. This is because the partial likelihood approach cannot eliminate the unknown cumulative base-line hazard functions in this setting. For coherent statistical inferences, a system of martingale processes is taken as a basis with which, together with the method of sieves, an overidentified estimating equation approach is proposed. A Pearson's χ2 type of goodness-of-fit testing statistic is derived as a by-product. An example with data on gastric cancer patients' survival times is analysed.
Fast Sampling of Gaussian Markov Random Fields
Authors: Rue Håvard
Published: March 2003

This paper demonstrates how Gaussian Markov random fields (conditional autoregressions) can be sampled quickly by using numerical techniques for sparse matrices. The algorithm is general and efficient, and expands easily to various forms for conditional simulation and evaluation of normalization constants. We demonstrate its use by constructing efficient block updates in Markov chain Monte Carlo algorithms for disease mapping.
Bayesian Calibration of Computer Models
Authors: Kennedy Marc C. , O'Hagan Anthony
Published: March 2003

We consider prediction and uncertainty analysis for systems which are approximated using complex mathematical models. Such models, implemented as computer codes, are often generic in the sense that by a suitable choice of some of the model's input parameters the code can be used to predict the behaviour of the system in a variety of specific applications. However, in any specific application the values of necessary parameters may be unknown. In this case, physical observations of the system in the specific context are used to learn about the unknown parameters. The process of fitting the model to the observed data by adjusting the parameters is known as calibration. Calibration is typically effected by ad hoc fitting, and after calibration the model is used, with the fitted input values, to predict the future behaviour of the system. We present a Bayesian calibration technique which improves on this traditional approach in two respects. First, the predictions allow for all sources of uncertainty, including the remaining uncertainty over the fitted parameters. Second, they attempt to correct for any inadequacy of the model which is revealed by a discrepancy between the observed data and the model predictions from even the best-fitting parameter values. The method is illustrated by using data from a nuclear radiation release at Tomsk, and from a more complex simulated nuclear accident exercise.
On Bayesian Consistency
Authors: Walker Stephen , Hjort Nils Lid
Published: March 2003

We consider a sequence of posterior distributions based on a data-dependent prior (which we shall refer to as a pseudoposterior distribution) and establish simple conditions under which the sequence is Hellinger consistent. It is shown how investigations into these pseudo posteriors assist with the understanding of some true posterior distributions, including Pólya trees, the infinite dimensional exponential family and mixture models.
Bootstrapping Survival Times in Stochastic Systems by Using Saddlepoint Approximations
Authors: Butler Ronald W. , Bronson Douglas A.
Published: March 2003

The single bootstrap is implemented by using a saddlepoint approximation to determine estimates for the survival and hazard functions of first-passage times in complicated semi-Markov processes. The double bootstrap is also implemented by resampling saddlepoint inversions and provides BCa confidence bands for these functions. Confidence intervals for the mean and variance of first-passage times are easily computed. A new characterization of the asymptotic hazard rate for survival times is presented and leads to an indirect method for constructing its bootstrap confidence interval.
A Direct Approach to False Discovery Rates
Authors: Storey John D.
Published: March 2003

Multiple-hypothesis testing involves guarding against much more complicated errors than single-hypothesis testing. Whereas we typically control the type I error rate for a single-hypothesis test, a compound error rate is controlled for multiple-hypothesis tests. For example, controlling the false discovery rate FDR traditionally involves intricate sequential p-value rejection methods based on the observed data. Whereas a sequential p-value method fixes the error rate and estimates its corresponding rejection region, we propose the opposite approach—we fix the rejection region and then estimate its corresponding error rate. This new approach offers increased applicability, accuracy and power. We apply the methodology to both the positive false discovery rate pFDR and FDR, and provide evidence for its benefits. It is shown that pFDR is probably the quantity of interest over FDR. Also discussed is the calculation of the q-value, the pFDR analogue of the p-value, which eliminates the need to set the error rate beforehand as is traditionally done. Some simple numerical examples are presented that show that this new approach can yield an increase of over eight times in power compared with the Benjamini–Hochberg FDR method.
On the Adequacy of Variational Lower Bound Functions for Likelihood-based Inference in Markovian Models with Missing Values
Authors: Hall Peter , Humphreys K. , Titterington D. M.
Published: March 2003

Variational methods have been proposed for obtaining deterministic lower bounds for log-likelihoods within missing data problems, but with little formal justification or investigation of the worth of the lower bound surfaces as tools for inference. We provide, within a general Markovian context, sufficient conditions under which estimators from the variational approximations are asymptotically equivalent to maximum likelihood estimators, and we show empirically, for the simple example of a first-order autoregressive model with missing values, that the lower bound surface can be very similar in shape to the true log-likelihood in non-asymptotic situations.
Approximate Likelihood Methods for Estimating Local Recombination Rates
Authors: Fearnhead Paul , Donnelly Peter
Published: March 2003

There is currently great interest in understanding the way in which recombination rates vary, over short scales, across the human genome. Aside from inherent interest, an understanding of this local variation is essential for the sensible design and analysis of many studies aimed at elucidating the genetic basis of common diseases or of human population histories. Standard pedigree-based approaches do not have the fine scale resolution that is needed to address this issue. In contrast, samples of deoxyribonucleic acid sequences from unrelated chromosomes in the population carry relevant information, but inference from such data is extremely challenging. Although there has been much recent interest in the development of full likelihood inference methods for estimating local recombination rates from such data, they are not currently practicable for data sets of the size being generated by modern experimental techniques. We introduce and study two approximate likelihood methods. The first, a marginal likelihood, ignores some of the data. A careful choice of what to ignore results in substantial computational savings with virtually no loss of relevant information. For larger sequences, we introduce a ‘composite’ likelihood, which approximates the model of interest by ignoring certain long-range dependences. An informal asymptotic analysis and a simulation study suggest that inference based on the composite likelihood is practicable and performs well. We combine both methods to reanalyse data from the lipoprotein lipase gene, and the results seriously question conclusions from some earlier studies of these data.
Perfect Samplers for Mixtures of Distributions
Authors: Casella G. , Mengersen K. L. , Robert C. P. , Titterington D. M.
Published: March 2003

We consider the construction of perfect samplers for posterior distributions associated with mixtures of exponential families and conjugate priors, starting with a perfect slice sampler in the spirit of Mira and co-workers. The methods rely on a marginalization akin to Rao–Blackwellization and illustrate the duality principle of Diebolt and Robert. A first approximation embeds the finite support distribution on the latent variables within a continuous support distribution that is easier to simulate by slice sampling, but we later demonstrate that the approximation can be very poor. We conclude by showing that an alternative perfect sampler based on a single backward chain can be constructed. This alternative can handle much larger sample sizes than the slice sampler first proposed.
Inference in Smoothing Spline Analysis of Variance
Authors: Guo Wensheng
Published: March 2003

Smoothing spline analysis of variance decomposes a multivariate function into additive components. This decomposition not only provides an efficient way to model a multivariate function but also leads to meaningful inference by testing whether a certain component equals 0. No formal procedure is yet available to test such a hypothesis. We propose an asymptotic method based on the likelihood ratio to test whether a functional component is 0. This test allows us to choose an optimal model and to compare groups of curves. We first develop the general theory by exploiting the connection between mixed effects models and smoothing splines. We then apply this to compare two groups of curves and to select an optimal model in a two-dimensional problem. A small simulation is used to assess the finite sample performance of the likelihood ratio test.
Adaptive Varying-Coefficient Linear Models
Authors: Fan Jianqing , Yao Qiwei , Cai Zongwu
Published: March 2003

Varying-coefficient linear models arise from multivariate nonparametric regression, non-linear time series modelling and forecasting, functional data analysis, longitudinal data analysis and others. It has been a common practice to assume that the varying coefficients are functions of a given variable, which is often called an index. To enlarge the modelling capacity substantially, this paper explores a class of varying-coefficient linear models in which the index is unknown and is estimated as a linear combination of regressors and/or other variables. We search for the index such that the derived varying-coefficient model provides the least squares approximation to the underlying unknown multidimensional regression function. The search is implemented through a newly proposed hybrid backfitting algorithm. The core of the algorithm is the alternating iteration between estimating the index through a one-step scheme and estimating coefficient functions through one-dimensional local linear smoothing. The locally significant variables are selected in terms of a combined use of the t-statistic and the Akaike information criterion. We further extend the algorithm for models with two indices. Simulation shows that the methodology proposed has appreciable flexibility to model complex multivariate non-linear structure and is practically feasible with average modern computers. The methods are further illustrated through the Canadian mink–muskrat data in 1925–1994 and the pound–dollar exchange rates in 1974–1983.
Comprehensive Definitions of Breakdown Points for Independent and Dependent Observations
Authors: Genton Marc G. , Lucas André
Published: March 2003

We provide a new definition of breakdown in finite samples, with an extension to asymptotic breakdown. Previous definitions centre on defining a critical region for either the parameter or the objective function. If for a particular outlier configuration the critical region is entered, breakdown is said to occur. In contrast with the traditional approach, we leave the definition of the critical region implicit. Our proposal encompasses previous definitions of breakdown in linear and non-linear regression settings. In some cases, it leads to a different and more intuitive notion of breakdown than other procedures that are available. An important advantage of our new definition is that it also applies to models for dependent observations where current definitions of breakdown typically fail. We illustrate our suggestion by using examples from linear and non-linear regression, and time series.