bluuebunny/crossref_metadata_2025 huggingface dataset:
The Causes of Unemployment in Post‐apartheid Johannesburg and the Livelihood Strategies of the Poor
Authors: Beall Jo , Crankshaw Owen , Parnell Susan
Published: March 2003

Central to the increase in urban poverty in the post‐apartheid period is the rise in unemployment. This provides the point of departure for this paper. The first section shows how Johannesburg and its environs, although constituting the industrial and commercial heartland of South Africa, is a city that has not reached its potential economic development. Having outlined the causes and dimensions of this sluggish economic position, next is considered how the poor survive in Johannesburg through both economic and non‐economic strategies. With this in mind it is argued that addressing the current situation of growing poverty and inequality (as well as redressing the legacy of past inequities) requires broad municipal response to urban unemployment. Instead of the current tendency to view poverty simply as the product of income and consumption deprivation, a more widely defined response to urban poverty reduction, based on a livelihoods framework, is proposed.
Refining Population Surface Models: Experiments with Northern Ireland Census Data
Authors: Martin David , Tate Nicholas J. , Langford Mitchel
Published: March 2003

This paper compares and contrasts alternative methods for the construction of discontinuous population surface models based on the census and remotely sensed data from Northern Ireland. Two main methods of population distribution are employed: (1) a method based on redistribution from enumeration district (ED) and postcode centroids, and (2) a method based on dasymetric redistribution of ED population counts to suitable land cover zones from classified remotely sensed imagery. Refinements have been made to the centroid redistribution algorithm to accommodate an empirical measure of dispersion, and to allow redistribution in an anisotropic form. These refinements are evaluated against each other and the dasymetric method. The results suggest that all of the methods perform best in urban areas, and that while the refinements may improve the statistical performance of the models, this is at the expense of reduced spatial detail. In general, the techniques are highly sensitive to the spatial and population resolution of the input data.
Capturing Raster Data From Scanned Thematic Maps Using Desktop Graphics Software
Authors: Wise Stephen
Published: March 2003

Data capture from paper maps remain a slow and costly part of many Geographic Information System projects. In this paper a simple method is described which makes use of the facilities of desktop graphics software to capture raster data from scanned thematic maps. The first stage is to use the flood fill tool to identify the regions of the map that represent the data values and set them to a separate colour for each thematic category. This edited image is then imported into a GIS, where a specially written majority filter is used to classify any remaining pixels to produce a raster GIS layer. The technique is tested on samples from three maps, giving accuracy levels of over 90% in all cases when compared with digitising the same maps by hand. The technique could be useful for situations where a rapid and simple means of data capture is needed and could be developed further by drawing on techniques for contextual classification rather than relying on a general purpose flood fill algorithm.
Binominal Noun Phrases in English
Authors: Aarts Bas
Published: March 2003

This paper discusses the structural and semantic properties of Binominal Noun Phrases (BNPs) in English. BNPs involve two nominals, N1 and N2, which are in a Subject‐Predicate relationship with each other, such that N1 is the Predicate and N2 the Subject. Examples are a hell of a problem, a wonder of a city, that idiot of a prime minister etc. On the basis of various types of syntactic evidence, it is argued that they are headed by the second of the two nominals, not by the first one, as has often been claimed. It is further argued that BNPs do not involve movement, as has recently been suggested in the literature. A consequence of this study is that it supports viewing syntax as a flexible system, in which there may be a tension between a rigid arrangement of elements into categories and constituents, and the occurrence of unexpected configurations, or of shifts in patterns taking place diachronically or synchronically.
Reviewing Proposals for a World Environmental Organisation
Authors: Lodefalk Magnus , Whalley John
Published: March 2003

Since the Earth Summit in Rio 1992, several calls have been made for a world environmental organisation (WEO), and only during the last year, in the run‐up to Rio+10, five more have been added. In total, we have found 17 proposals for a WEO. We review, compare, and briefly discuss rationales, models, tasks, organisational set‐up, relations to multilateral environmental agreements (MEAs) and organisations such as UNEP and the WTO, as well as the role of principles, compliance and the interest of developing countries. We conclude that a majority of proposers is in favour of an autonomous coordinating agency, that is, a medium level of integration. Frequently the WTO is mentioned as a precursor agency on which a WEO should be based. We question the effectiveness of a ‘WTO for the environment’ and suggest that other models ought to be considered.
Trade in Educational Services: Trends and Emerging Issues
Authors: Larsen Kurt , Martin John P. , Morris Rosemary
Published: March 2003

This paper examines the trends and emerging issues in trade in educational services. It provides rough estimates of the size of the international market in educational services drawing on the limited data available in services trade statistics and data on foreign students in tertiary education in OECD countries. It outlines the current commitments for trade in educational services under the General Agreement on Trade in Services (GATS). It also reviews the implications of the on‐going GATS negotiations for further multilateral trade liberalisation in this sector. It points out that OECD countries have been noticeably reluctant to make proposals for further liberalisation of trade in educational services. One reason for this is the concern in many countries about the potential threats posed to cultural values and national traditions by growing trade liberalisation in educational services. Finally, the paper reviews some of the main policy issues arising from trade in educational services.
Linguistic Human Rights and English in Europe
Authors: Phillipson Robert , Skutnabb‐Kangas Tove
Published: March 2003

This paper looks at policies of linguistic expansion worldwide, in particular at English in the colonial and postcolonial periods. It addresses the issue of whether the expansion of English in continental Europe represents a threat or a blessing. It considers some of the ambiguities in English being promoted, particularly in connection with ESL expertise, as a language serving ‘international’ purposes and simultaneously British and American interests. It considers the attitude of continental European scientists to needing to publish in English and implications for the ecology of languages in Europe.
‘We were all thegither . . . I think we was all thegither’:was regularization in Buckie English
Authors: Smith Jennifer , Tagliamonte Sali
Published: March 2003

Variation in the past tense paradigm of the verb be (e.g., I were, you was, we was) is widespread amongst English dialects, and is often considered to be the result of analogical levelling. Through an analysis of non‐standard was in Buckie English, a variety spoken in a small fishing town in north‐east Scotland, we show that the historical record provides the most relevant perspective on the variation. 2nd person singular you, 1st person plural we, plural NPs and existentials highly favour was, however, 3rd person plural they demonstrates categorical use of were. The constraint hierarchy across grammatical person and subject type reflect the most widely‐cited patterns mentioned in the historical literature. These findings demonstrate that a relatively isolated community provides an imprint of the past in the present, the tracks of which have been strikingly preserved by longitudinal continuity of the idiosyncrasies of the verb be.
The relative clause in colloquial Singapore English
Authors: Alsagoff Lubna , Lick Ho Chee
Published: March 2003

In this paper, we demonstrate the specific ways in which the influence of Chinese manifests itself in the structure of the noun phrases containing relative clause modifiers in colloquial Singapore English. We argue that while previous researchers have been correct in pointing out the substratal influence of Chinese, they have not gone far enough in articulating the specific nature of this influence, in particular on the grammar. Colloquial Singapore English relative clauses are interesting because they show an amalgamation of both substrate and superstrate grammatical features. This blending of features is a precise one in which substrate influence is in some way regulated and limited by the superstrate grammar. The combination of superstrate and substrate grammars is illustrated in the constituent ordering of relative clause modifiers, as well as the grammatical behavior of the relative pronoun one. In this paper, we also seek to show that colloquial Singapore English relative clauses are extremely elaborate grammatical structures which argue against new varieties of English being characterized as simplified versions of their superstrate language
Pitch accent in Indian‐English teaching discourse
Authors: Pickering Lucy , Wiltshire Caroline
Published: March 2003

The phonetic correlates of accent/stress distinguish Indian English (IE) from American dialects (Spencer, 1957; Kachru, 1983). We examine the realization of accent in IE compared to American English (AE) produced by teaching assistants in similar contexts. In teaching discourse, we find that a lexically accented syllable is often realized in IE with a relative drop in frequency and without a reliable increase in amplitude. In similar contexts, lexically accented syllables in AE reliably increase in both frequency and amplitude. Following the distinction made in Beckman (1986), we conclude that IE acts as a pitch‐accent language rather than as a stress‐accent language like AE. We also suggest a source for the distinct prosodics of IE: some Indian languages use a low pitch on accented syllables (Mohanan, 1986; Hayes and Lahiri, 1991; Harnsberger, 1999). We investigate the effect of different first languages on the production of IE using three Indian teaching assistants with different L1 (Bengali, Tamil, Hindi‐Urdu), and compare their IE discourse to L1 sentences. The similarity of the results for three different L1 suggests that the phonetic correlates of accent in IE are common to Indian languages.
Transcending the nativeness paradigm
Authors: Brutt‐Griffler Janina , Samimy Keiko K.
Published: March 2003

This study suggests that identity‐formation is related to the social process of identity‐assignation in the mother tongue context. The case studies of four English speakers are summarized in this study. The four English speakers, who were all born outside the mother tongue context, bend categories in various ways. This uncovers the ways in which mother tongue speakers situate other English users and how such social attitudes help shape the identities of those users. The findings support the contention that nativeness and nonnativeness among English users constitute non‐elective socially constructed identities rather than linguistic categories.
Legislation and Non‐neutral Principles: A Lockean Approach
Authors: Tuckness Alex
Published: March 2003

When citizens and legislators attempt to justify coercive acts, such as fines or imprisonment, they often do so on the basis of controversial justificatory principles. There are at least two ways a principle can be controversial: one may claim that the principle in question is false; or one may claim that the principle, correctly applied, does not actually justify the specific act in question. Thus, suppose the state invokes the principle ‘false beliefs should be censored’ to justify silencing a dissident. The dissident might disagree because she thinks the state should not be in the business of censoring false beliefs, or she might agree with the principle but object to the action because she is quite convinced that her beliefs are not false.
Multiple Equilibria in the Citizen‐Candidate Model of Representative Democracy
Authors: Dhillon Amrita , Lockwood Ben
Published: March 2003

The Besley‐Coate model of representative democracy has the problem of multiple equilibria (Besley‐Coate 1997). We show that requiring the Besley‐Coate political equilibria to be iteratively undominated at the voting stage refines the set of (pure strategy) political equilibrium outcomes only for those cases where at least four candidates stand for election. This note complements the results of De Sinopoli and Turrini (1999).
A Macroeconomic Analysis of Publicly Funded Health Care
Authors: Bednarek Heather L. , Pecchenino Rowena A.
Published: March 2003

In a general equilibrium, overlapping generations framework this paper examines how the tax‐benefit system that underlies the U.S. health care system affects the well‐being of different age groups, and the lifetime well‐being of different socioeconomic groups, as well as society as a whole. We find that the optimal set and generosity of publicly funded health care programs is sensitive to the social welfare function and to the prices that various agents in society pay for medical care. Social welfare under the current financing system is also compared to alternative financing mechanisms such as Medical Savings Accounts.
Towards a Characterization of Second‐Best Pure Strategy Solutions to a Smooth and Symmetric Partnership Problem
Authors: Filipovich Dragan
Published: March 2003

This article makes a start in characterizing the second‐best solution to a smooth, symmetric partnership problem. It derives a more tractable formulation of the problem using a modified version of the condition in Legros and Matthews (1993). Then it uses this formulation to show that the second‐best solution will depend crucially on the curvature (third derivatives) of the production and disutility schedules. Moreover, it shows that the residual claimant solution will be second‐best for sufficiently large partnerships.
Determining Market Areas Captured by Competitive Facilities: A Continuous Equilibrium Modeling Approach
Authors: Wong Sze‐Chun , Yang Hai
Published: March 2003

Many existing models concerning locations and market areas of competitive facilities assume that customers patronize a facility based on distance to that facility, or perhaps on a function of distances between the customer and the different facilities available. Customers are generally assumed to be located at certain discrete demand points in a two‐dimensional space, or continuously distributed over a one‐dimensional line segment. In this paper these assumptions are relaxed by employment of a continuum optimization model to characterize the equilibrium choice behavior of customers for a given set of competitive facilities over a heterogeneous two‐dimensional space. Customers are assumed to be scattered continuously over the space and each customer is assumed to choose a facility based on both congested travel time to the facility and on the attributes of the facility. The model is formulated as a calculus of variations problem and its optimality conditions are shown to be equivalent to the spatial customer‐choice equilibrium conditions. An efficient numerical method using finite element technique is proposed and illustrated with a numerical example.
The Return of Zipf: Towards a Further Understanding of the Rank‐Size Distribution
Authors: Brakman Steven , Garretsen Harry , Van Marrewijk Charles , Van Den Berg Marianne
Published: March 2003

We offer a general‐equilibrium economic approach to Zipf's Law or, more generally, the rank‐size distribution—the striking empirical regularity concerning the size distribution of cities. We provide some further understanding of Zipf's Law by incorporating negative feedbacks (congestion) in a popular model of economic geography and international trade. This model allows the powers of agglomeration and spreading to be in long‐run equilibrium, which enhances our understanding of the existence of a rank‐size distribution of cities.
The Differential Regional Effects of Monetary Policy: Evidence from the U.S. States
Authors: Carlino Gerald , DeFina Robert
Published: March 2003

In this paper we use time‐series techniques to examine whether monetary policy had symmetric effects across U.S. states during the 1958:1–1992:4 period. Impulse response functions from estimated structural vector autoregression models reveal differences in policy responses, which in some cases are substantial. We provide evidence on the reasons for the measured cross‐state differential policy responses. The size of a state's response is significantly related to industry‐mix variables, providing evidence of an interest rate channel for monetary policy, although the state‐level data offer no support for recently advanced credit‐channel theories.
A Methodology for Estimating Returns to Skills for Canadian Provinces and U.S. States
Authors: Hunt Gary L. , Mueller Richard E.
Published: March 2003

Differences in both regional skill prices and skill mix can explain interregional variations in wage distributions. We control for interregional differences in skill mix that permit us to compute key parameters of regional wage distributions including regional returns to skills. In addition to setting forth the methods in detail, we also present estimates for 48 U.S. states and 10 Canadian provinces. For both males and females, we find that regional mean wages (with controls for skills mix) in the U.S. and Canada are similar, but that the returns to skills are systematically higher in the U.S.
Spillover Effects of Welfare Reforms in State Labor Markets
Authors: Bartik Timothy J.
Published: March 2003

This paper estimates the effects of welfare reforms on a state’s employment and wage rates. Welfare reforms include: pushing welfare recipients into the labor force, financial incentives to recipients for working, wage subsidies to employers of recipients, and community service jobs for recipients. The effects of these policies are analyzed using a newly estimated model of state labor markets. Simulations show that jobs found by welfare reform participants cause sizable displacement effects for nonparticipants. Displacement effects of labor supply policies are highest when a state’s unemployment is high, whereas displacement effects of labor demand policies are highest when a state’s unemployment is low.
Using Excise Taxes to Finance State Government: Do Neighboring State Taxation Policy and Cross‐Border Markets Matter?
Authors: Nelson Michael A.
Published: March 2003

In this paper the excise tax policy of U.S. state governments is analyzed with special attention to how this policy is influenced by the level of excise taxation in neighboring states, “border‐tax effects,” and the relative size of the market located across state boundaries. Using a panel data set, state policies towards the taxation of cigarettes, all alcoholic beverages, beer, distilled liquor, motor fuel, and insurance are investigated within the context of a vote‐maximizing model of collective decision making. The role of the industry in that state whose goods and services are singled out for special taxation is also examined.
A pre‐school training programme for children with poor phonological awareness: effects on reading and spelling
Authors: Layton Lyn , Deeny Karen , Upton Graham , Tall Graham
Published: March 2003

An earlier paper published in this journal described the pilot study and first two phases of a longitudinal study that examined the possibility of preventing the emergence of written language difficulties, by addressing the ability of pre‐schoolers to make phonological judgements (Layton, Deeny, Upton and Tall, 1996). The literacy development of the children involved in the study was assessed when they had been in mainstream education for approximately two years. It was discovered that there were no significant differences, in terms of written language achievement, between the children who had received phonological training while in nursery school and their peers in a control group whose training programme had not featured phonological awareness activities. These findings challenge the view that training pre‐schoolers to attend to the sound structure of words promotes later literacy development. The results are considered in the context of other research findings, and then the study is discussed in both quantitative and qualitative terms, with some comment on the feasibility of identifying pre‐schoolers at risk for literacy failure on the basis of poor phonological awareness.
Causal connections in beginning reading: the importance of rhyme
Authors: Goswami Usha
Published: March 2003

Profound misunderstandings of the implications of rhyme and analogy research (sometimes called ‘new phonics’) for classroom teaching still appear regularly in the reading literature. It has been argued that ‘rhyme and analogy’ researchers do not believe in teaching children grapheme‐phoneme correspondences (Chew, 1997). Rhyme and analogy has also been branded as ‘analytic phonics’, which is argued to be inferior to ‘synthetic’ phonics (Watson and Johnston, 1999). Such misconceptions are confusing the debate over how best to teach ‘phonics’, following the publication of the National Literacy Framework (DfEE, 1998). For example, some authors are suggesting that teachers should replace an emphasis on phonological awareness and onset‐rime with a teaching programme based on ‘synthetic’ phonics (Deavers and Solity, 1998; Watson and Johnston, 1999). This paper discusses the implications of Goswami and Bryant’s (1990) theory about important causal connections in reading for classroom teaching, and reviews more recent ‘rhyme and analogy’ research within this framework. New research on the nature of the English spelling system and the representation of linguistic knowledge is also discussed. The importance of taking a balanced approach to phonics instruction and teaching children correspondences between letters and phonemes and letter sequences and rimes is emphasised.
Evaluation of a computer‐based reading intervention in infant and junior schools
Authors: Nicolson Roderick , Fawcett Angela , Nicolson Margaret
Published: March 2003

Recent studies (Fawcett et al, 1999; Nicolson et al, 1999) have demonstrated that 6 and 8 year old children found to be at risk of reading failure can be provided with very cost‐effective support using traditional teaching methods. Nonetheless, a significant minority of children failed to make sufficient progress. The present studies undertook a replication of these studies, using the RITA computer‐based literacy support system. The RITA system assists, rather than replaces, the teacher in providing support tailored to each child’s profile of reading attainments. The results indicated that the RITA support was both educationally effective and economically effective, with comparable cost effectiveness to the traditional approach when used with infant school children (6 year olds), and somewhat greater cost effectiveness when used with junior school children (8 year olds). All groups of children reacted very positively to the RITA lessons. It is suggested that computer‐assisted reading support can be effective in supporting children at risk of reading failure, even at junior school level.
Typography in children’s reading schemes may be suboptimal: Evidence from measures of reading rate
Authors: Hughes Laura , Wilkins Arnold
Published: March 2003

We investigated whether the layout of type in two popular children’s reading schemes was suitable for the intended reading age. 120 children read four passages of text that adopted the typography of four reading stages in each of the two schemes. The size and spacing of the texts decreased with successive stages as the intended reading age increased. The reading speed of children aged 5 to 7 years decreased as the text size decreased: in particular, these children read fastest the text designed for 5 and 6 year olds. Older children aged 8 to 11 years were neither assisted nor disadvantaged by text size. Children of all ages, particularly those susceptible to visual stress, were found to make more errors on the smaller than on the larger text. We conclude that the reading development of some children might benefit from a larger text size and spacing than is currently the norm, and that no children would be disadvantaged by such a change.
The construction of literate understanding in a literature‐based classroom
Authors: Fang Zhihui
Published: March 2003

This study investigated young children’s developing understanding of three essential features of book language (i.e. autonomy, conventionality, unique grammar) in two curricular genres (i.e. narrative and expository) in a literature‐based, multigrade (1st–3rd) classroom. Each of the 19 participants was asked to compose two written texts (story and report) at beginning, middle and end of the school year. All texts were coded for inclusion of a variety of genre‐specific discursive markers that index the three features of book language. Analyses showed that (a) the children demonstrated emergent understanding of autonomy, limited familiarity with conventionality and an embryonic sense of unique grammar, irrespective of genre; (b) they gained significantly more understanding of the three book‐language features in both curricular genres over the school year; (c) the development of this understanding is genre‐ and feature‐specific, unstable, complex and not consistently associated with children’s grade level. These findings were interpreted from both developmental and pedagogical perspectives. Limitations and directions for future research were also discussed.
Sampling Frame Effects on the British Crime Survey
Authors: Lynn Peter
Published: March 2003

In 1992, the British Crime Survey used the postcode address file as the sampling frame for the first time, having previously used the electoral registers (ERs). This paper addresses concerns that the change in frame may have affected the survey data, particularly measures of change over time in victimization rates. The general conclusion is that the change may have caused increases in crime rates between 1988 and 1992 to be slightly overestimated, but only by an amount which is very small compared with other sources of survey error. Information is also provided on the nature of the biased coverage of the ERs, and the population subgroups that would be under-represented by surveys involving ER samples.
Accounting for Inaccuracies in Population Counts and Case Registration in Cancer Mapping Studies
Authors: Best N. , Wakefield Jon
Published: March 2003

Disease mapping studies summarize spatial and spatiotemporal variations in disease risk. This information may be used for simple descriptive purposes, to assess whether health targets are being met or whether new policies are successful, to provide the context for further studies (by providing information on the form and size of the spatial variability in risk) or, by comparing the estiamted risk map with an exposure map, to obtain clues to aetiology. There are well-known problems with mapping raw risks and relative risks for rare diseases and/or small areas since sampling variability tends to dominate the subsequent maps. To alleviate these difficulties a multilevel modelling approach may be followed in which estimates based on small numbers are ‘shrunk’ towards a common value. In this paper we extend these models to investigate the effects of inaccuracies in the health and population data. In terms of the health data we consider the effects of errors that occur due to the imperfect collection procedures that are used by disease registers. For cancers in particular, this is a major problem, with case underascertainment (i.e. undercount) being the common type of error. The populations that are used for estimating disease risks have traditionally been treated as known quantities. In practice, however, these counts are often based on sources of data such as the census which are subject to error (in particular underenumeration) and are only available for census years. Intercensual population counts must consider not only the usual demographic changes (e.g. births and deaths) but migration also. We propose several approaches for modelling population counts and investigate the sensitivity of inference to the sizes of these errors. We illustrate the methods proposed using data for breast cancer in the Thames region of the UK and we compare our results with those obtained from more conventional approaches.
Multilevel Models for Repeated Binary Outcomes: Attitudes and Voting over the Electoral Cycle
Authors: Yang Min , Goldstein H. , Heath A.
Published: March 2003

Models for fitting longitudinal binary responses are explored by using a panel study of voting intentions. A standard multilevel repeated measures logistic model is shown to be inadequate owing to a substantial proportion of respondents who maintain a constant response over time. A multivariate binary response model is shown to be a better fit to the data.
Investigating the Economic and Demographic Determinants of Sporting Participation in England
Authors: Farrell Lisa , Shields Michael A.
Published: March 2003

We provide a detailed statistical investigation into the economic and demographic factors that determine sporting participation in England. Using data from the 1997 health survey of England we fit random-effects probit models that take into account unobservable household preferences for sporting activities, as well as the economic and demographic characteristics of respondents. Our main results from the multivariate analysis are that sporting participation is positively related to household income, the educated participate in sports to a greater extent than the uneducated, there is no evidence of regional differentials in sporting participation and household preferences play an important role in the decision to participate in sports.
Causal Variables, Indicator Variables and Measurement Scales: An Example from Quality of Life
Authors: Fayers Peter M. , Hand David J.
Published: March 2003

There is extensive literature on the development and validation of multi-item measurement scales. Much of this is based on principles derived from psychometric theory and assumes that the individual items form parallel tests, so that simple weighted or unweighted summation is an appropriate method of aggregation. More recent work either continues to promulgate these methods or places emphasis on modern techniques centred on item response theory. In fact, however, clinical measuring instruments often have different underlying principles, so adopting such approaches is inappropriate. We illustrate, using health-related quality of life, that clinimetric and psychometric ideas need to be combined to yield a suitable measuring instrument. We note the fundamental distinction between indicator and causal variables and propose that this distinction suffices to explain fully the need for both clinimetric and psychometric techniques, and identifies their respective roles in scale development, validation and scoring.
On the Optimality of Prediction-based Selection Criteria and the Convergence Rates of Estimators
Authors: Altman Naomi , Léger Christian
Published: March 2003

Several estimators of squared prediction error have been suggested for use in model and bandwidth selection problems. Among these are cross-validation, generalized cross-validation and a number of related techniques based on the residual sum of squares. For many situations with squared error loss, e.g. nonparametric smoothing, these estimators have been shown to be asymptotically optimal in the sense that in large samples the estimator minimizing the selection criterion also minimizes squared error loss. However, cross-validation is known not to be asymptotically optimal for some ‘easy' location problems. We consider selection criteria based on estimators of squared prediction risk for choosing between location estimators. We show that criteria based on adjusted residual sum of squares are not asymptotically optimal for choosing between asymptotically normal location estimators that converge at rate n1/2but are when the rate of convergence is slower. We also show that leave-one-out cross-validation is not asymptotically optimal for choosing between √n-differentiable statistics but leave-d-out cross-validation is optimal when d→∞ at the appropriate rate.
Prior Distributions on Measure Space
Authors: Sibisi Sibusiso , Skilling John
Published: March 2003

A measure is the formal representation of the non-negative additive functions that abound in science. We review and develop the art of assigning Bayesian priors to measures. Where necessary, spatial correlation is delegated to correlating kernels imposed on otherwise uncorrelated priors. The latter must be infinitely divisible (ID) and hence described by the Lévy–Khinchin representation. Thus the fundamental object is the Lévy measure, the choice of which corresponds to different ID process priors. The general case of a Lévy measure comprising a mixture of assigned base measures leads to a prior process comprising a convolution of corresponding processes. Examples involving a single base measure are the gamma process, the Dirichlet process (for the normalized case) and the Poisson process. We also discuss processes that we call the supergamma and super-Dirichlet processes, which are double base measure generalizations of the gamma and Dirichlet processes. Examples of multiple and continuum base measures are also discussed. We conclude with numerical examples of density estimation.
Analysis of Longitudinal Binary Data from Multiphase Sampling
Authors: Clayton David , Spiegelhalter David , Dunn Graham , Pickles Andrew
Published: March 2003

The efficient use of surrogate or auxiliary information has been investigated within both model-based and design-based approaches to data analysis, particularly in the context of missing data. Here we consider the use of such data in epidemiological studies of disease incidence in which surrogate measures of disease status are available for all subjects at two time points, but definitive diagnoses are available only in stratified subsamples. We briefly review methods for the analysis of two-phase studies of disease prevalence at a single time point, and we discuss the extension of four of these methods to the analysis of incidence studies. Their performance is compared with special reference to a study of the incidence of senile dementia.
Bias-corrected Confidence Bands in Nonparametric Regression
Authors: Xia Yingcun
Published: March 2003

Bias-corrected confidence bands for general nonparametric regression models are considered. We use local polynomial fitting to construct the confidence bands and combine the cross-validation method and the plug-in method to select the bandwidths. Related asymptotic results are obtained. Our simulations show that confidence bands constructed by local polynomial fitting have much better coverage than those constructed by using the Nadaraya–Watson estimator. The results are also applicable to nonparametric autoregressive time series models.
Missing Covariates in Generalized Linear Models When the Missing Data Mechanism is Non-ignorable
Authors: Ibrahim Joseph G. , Lipsitz Stuart R. , Chen Ming-Hui
Published: March 2003

We propose a method for estimating parameters in generalized linear models with missing covariates and a non-ignorable missing data mechanism. We use a multinomial model for the missing data indicators and propose a joint distribution for them which can be written as a sequence of one-dimensional conditional distributions, with each one-dimensional conditional distribution consisting of a logistic regression. We allow the covariates to be either categorical or continuous. The joint covariate distribution is also modelled via a sequence of one-dimensional conditional distributions, and the response variable is assumed to be completely observed. We derive the E- and M-steps of the EM algorithm with non-ignorable missing covariate data. For categorical covariates, we derive a closed form expression for the E- and M-steps of the EM algorithm for obtaining the maximum likelihood estimates (MLEs). For continuous covariates, we use a Monte Carlo version of the EM algorithm to obtain the MLEs via the Gibbs sampler. Computational techniques for Gibbs sampling are proposed and implemented. The parametric form of the assumed missing data mechanism itself is not ‘testable' from the data, and thus the non-ignorable modelling considered here can be viewed as a sensitivity analysis concerning a more complicated model. Therefore, although a model may have ‘passed' the tests for a certain missing data mechanism, this does not mean that we have captured, even approximately, the correct missing data mechanism. Hence, model checking for the missing data mechanism and sensitivity analyses play an important role in this problem and are discussed in detail. Several simulations are given to demonstrate the methodology. In addition, a real data set from a melanoma cancer clinical trial is presented to illustrate the methods proposed.
Generalized Spectral Tests for Serial Dependence
Authors: Hong Yongmiao
Published: March 2003

Two tests for serial dependence are proposed using a generalized spectral theory in combination with the empirical distribution function. The tests are generalizations of the Cramér-von Mises and Kolmogorov-Smirnov tests based on the standardized spectral distribution function. They do not involve the choice of a lag order, and they are consistent against all types of pairwise serial dependence, including those with zero autocorrelation. They also require no moment condition and are distribution free under serial independence. A simulation study compares the finite sample performances of the new tests and some closely related tests. The asymptotic distribution theory works well in finite samples. The generalized Cramér-von Mises test has good power against a variety of dependent alternatives and dominates the generalized Kolmogorov-Smirnov test. A local power analysis explains some important stylized facts on the power of the tests based on the empirical distribution function.
Dealing With Label Switching in Mixture Models
Authors: Stephens Matthew
Published: March 2003

In a Bayesian analysis of finite mixture models, parameter estimation and clustering are sometimes less straightforward than might be expected. In particular, the common practice of estimating parameters by their posterior mean, and summarizing joint posterior distributions by marginal distributions, often leads to nonsensical answers. This is due to the so-called ‘label switching’ problem, which is caused by symmetry in the likelihood of the model parameters. A frequent response to this problem is to remove the symmetry by using artificial identifiability constraints. We demonstrate that this fails in general to solve the problem, and we describe an alternative class of approaches, relabelling algorithms, which arise from attempting to minimize the posterior expected loss under a class of loss functions. We describe in detail one particularly simple and general relabelling algorithm and illustrate its success in dealing with the label switching problem on two examples.
Following a Moving Target—Monte Carlo Inference for Dynamic Bayesian Models
Authors: Gilks Walter R. , Berzuini Carlo
Published: March 2003

Markov chain Monte Carlo (MCMC) sampling is a numerically intensive simulation technique which has greatly improved the practicality of Bayesian inference and prediction. However, MCMC sampling is too slow to be of practical use in problems involving a large number of posterior (target) distributions, as in dynamic modelling and predictive model selection. Alternative simulation techniques for tracking moving target distributions, known as particle filters, which combine importance sampling, importance resampling and MCMC sampling, tend to suffer from a progressive degeneration as the target sequence evolves. We propose a new technique, based on these same simulation methodologies, which does not suffer from this progressive degeneration.
A Measure of Disclosure Risk for Microdata
Authors: Skinner C. J. , Elliot M. J.
Published: March 2003

Protection against disclosure is important for statistical agencies releasing microdata files from sample surveys. Simple measures of disclosure risk can provide useful evidence to support decisions about release. We propose a new measure of disclosure risk: the probability that a unique match between a microdata record and a population unit is correct. We argue that this measure has at least two advantages. First, we suggest that it may be a more realistic measure of risk than two measures that are currently used with census data. Second, we show that consistent inference (in a specified sense) may be made about this measure from sample data without strong modelling assumptions. This is a surprising finding, in its contrast with the properties of the two ‘similar’ established measures. As a result, this measure has potentially useful applications to sample surveys. In addition to obtaining a simple consistent predictor of the measure, we propose a simple variance estimator and show that it is consistent. We also consider the extension of inference to allow for certain complex sampling schemes. We present a numerical study based on 1991 census data for about 450 000 enumerated individuals in one area of Great Britain. We show that the theoretical results on the properties of the point predictor of the measure of risk and its variance estimator hold to a good approximation for these data.
Bovine Spongiform Encephalopathy Maternal Cohort Study—Exploratory Analysis
Authors: Gore Sheila M. , Gilks Walter R. , Wilesmith John W.
Published: March 2003

The bovine spongiform encephalopathy (BSE) maternal cohort study supports a role both for direct maternal transmission and for inherited genetic susceptibilty to the BSE agent. Additional data from the main BSE database do not resolve whether the risk of direct maternal transmission of BSE from dam to calf is concentrated in the interval within 5 months before the onset of BSE in the dam, as data from the BSE maternal cohort study suggest. The reason for this is that we cannot rely, as our analysis requires, on the survival of calves or traceability of the dam being independent of the interval from the birth of a calf to onset of BSE in the dam. Accordingly, for the present, we place most weight on evidence from the BSE maternal cohort study. Direct maternal transmission of the BSE agent from dam to calf has not been ruled out; vertical transmission of the new variant Creutzfeldt–Jakob disease (NVCJD) from mother with NVCJD to baby is therefore also possible. Actions to quantify, and minimize, the transmission risk, if any, from a mother with NVCJD to her baby, or to delivery teams, should be taken without delay.
Analysis of the Bovine Spongiform Encephalopathy Maternal Cohort Study: The Discordant Case–Control Pairs
Authors: Curnow R. N. , Hodge A. , Wilesmith J. W.
Published: March 2003

The progeny of the affected and non-affected dams in the bovine spongiform encephalopathy (BSE) cohort study were paired in terms of their farm of origin and approximate date of birth. This paper presents an exact logistic regression analysis that avoids modelling the differences between the pairs and so analyses only the discordant pairs. There is some evidence that the pairs in which the affected animal was born to the affected dam tend to be those in which the onset of BSE in the affected dam preceded or occurred soon after the calving. This suggests some occurrence of maternal transmission.
Software Reliability Assessment using Accelerated Testing Methods
Authors: Ehrlich Willa K. , Nair Vijayan N. , Alam M. S. , Chen W. H. , Engel Mark
Published: March 2003

The use of operational profiles and usage-based testing has received considerable attention recently in the software engineering literature. Testing under the actual operational profile can, however, be expensive, time consuming or even infeasible in situations where the performance of a system is dominated by infrequent but highly critical events. We consider a real application that deals with telecommunications network restoration after network failure caused by cuts in fibre optic cables. We use this application to demonstrate the usefulness of traditional accelerated testing methods to test and estimate software reliability. These methods, which have been extensively used in hardware reliability, have an important role to play in software reliability assessment as well.
Using Quantile Plots of the Prediction Variance for Comparing Designs for a Constrained Mixture Region: An Application Involving a Fertilizer Experiment
Authors: Khuri André I. , Harrison Jay M. , Cornell John A.
Published: March 2003

Summary. Vining and co-workers have used plots of the prediction variance trace (PVT) along the so-called prediction rays to compare mixture designs in a constrained region R. In the present paper, we propose a method for describing the distribution of the prediction variance within the region R by using quantile plots. More comprehensive comparisons between mixture designs are possible through the proposed plots than with the PVT plots. The utility of the quantile plots is illustrated with a four-component fertilizer experiment that was initiated in São Paulo, Brazil.
Proportional Hazards Models: A Latent Competing Risk Approach
Authors: Gelfand Alan E. , Ghosh Sujit K. , Christiansen Cindy , Soumerai Stephen B. , McLaughlin Thomas J.
Published: March 2003

We propose a novel semiparametric version of the widely used proportional hazards survival model. Features include an arbitrarily rich class of continuous base-line hazards, an attractive epidemiological interpretation of the hazard as a latent competing risk model and trivial handling of censoring. Models are fitted by using a data augmentation scheme. The methodology is applied to a data set recording times to first hospitalization following clinical diagnosis of acquired immune deficiency syndrome for a sample of 169 patients.
Anisotropic Spatial Sampling Designs for Urban Pollution
Authors: Arbia Giuseppe , Lafratta Giovanni
Published: March 2003

Isotropic processes form an inadequate basis in modelling many spatially distributed data. In particular environmental phenomena often have strong anisotropic spatial variation, especially when the regions monitored are very large. We extend a recently proposed optimal sampling strategy by assuming a spatial anisotropic random field as the basis for the data generator mechanism. The procedure is based on a geographical space transformation indicated by Sampson and Guttorp. We discuss the optimal design and we develop a sequential procedure for selecting a network of monitoring stations in environmental surveys. Some data on sulphur dioxide pollution in Padua (Italy) are analysed to illustrate the method.