Página 13 dos resultados de 1256 itens digitais encontrados em 0.014 segundos

The existence and asymptotic properties of a backfitting projection algorithm under weak conditions

Linton, Oliver; Mammen, E.; Nielsen, J.
Fonte: London School of Economics and Political Science Research Publicador: London School of Economics and Political Science Research
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em //1999 Português
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We derive the asymptotic distribution of a new backfitting procedure for estimating the closest additive approximation to a nonparametric regression function. The procedure employs a recent projection interpretation of popular kernel estimators provided by Mammen, Marron, Turlach and Wand and the asymptotic theory of our estimators is derived using the theory of additive projections reviewed in Bickel, Klaassen, Ritov and Wellner. Our procedure achieves the same bias and variance as the oracle estimator based on knowing the other components, and in this sense improves on the method analyzed in Opsomer and Ruppert. We provide ‘‘high level’’ conditions independent of the sampling scheme. We then verify that these conditions are satisfied in a regression and a time series autoregression under weak conditions.

On a semiparametric survival model with flexible covariate effect

Nielsen, Jens P.; Linton, Oliver; Bickel, Peter J.
Fonte: London School of Economics and Political Science Research Publicador: London School of Economics and Political Science Research
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em //1998 Português
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A semiparametric hazard model with parametrized time but general covariate dependency is formulated and analyzed inside the framework of counting process theory. A profile likelihood principle is introduced for estimation of the parameters: the resulting estimator is n1/2-consistent, asymptotically normal and achieves the semiparametric efficiency bound. An estimation procedure for the nonparametric part is also given and its asymptotic properties are derived. We provide an application to mortality data.

Large-sample inference for nonparametric regression with dependent errors

Robinson, Peter M.
Fonte: London School of Economics and Political Science Research Publicador: London School of Economics and Political Science Research
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em //1997 Português
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A central limit theorem is given for certain weighted partial sums of a covariance stationary process, assuming it is linear in martingale differences, but without any restriction on its spectrum. We apply the result to kernel nonparametric fixed-design regression, giving a single central limit theorem which indicates how error spectral behavior at only zero frequency influences the asymptotic distribution and covers long-range, short-range and negative dependence. We show how the regression estimates can be Studentized in the absence of previous knowledge of which form of dependence pertains, and show also that a simpler Studentization is possible when long-range dependence can be taken for granted.

Narrow-band analysis of nonstationary processes

Marinucci, D.; Robinson, Peter M.
Fonte: London School of Economics and Political Science Research Publicador: London School of Economics and Political Science Research
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em //2001 Português
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The behavior of averaged periodograms and cross-periodograms of a broad class of nonstationary processes is studied. The processes include nonstationary ones that are fractional of any order, as well as asymptotically stationary fractional ones. The cross-periodogram can involve two nonstationary processes of possibly different orders, or a nonstationary and an asymptotically stationary one. The averaging takes place either over the whole frequency band, or over one that degenerates slowly to zero frequency as sample size increases. In some cases it is found to make no asymptotic difference, and in particular we indicate how the behavior of the mean and variance changes across the two-dimensional space of integration orders. The results employ only local-to-zero assumptions on the spectra of the underlying weakly stationary sequences. It is shown how the results can be applied in fractional cointegration with unknown integration orders.

Second-order approximation for adaptive regression estimators

Linton, Oliver; Xiao, Zhijie
Fonte: Cambridge University Press Publicador: Cambridge University Press
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em /10/2001 Português
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We derive asymptotic expansions for semiparametric adaptive regression estimators. In particular, we derive the asymptotic distribution of the second-order effect of an adaptive estimator in a linear regression whose error density is of unknown functional form. We then show how the choice of smoothing parameters influences the estimator through higher order terms. A method of bandwidth selection is defined by minimizing the second-order mean squared error. We examine both independent and time series regressors; we also extend our results to a t-statistic. Monte Carlo simulations confirm the second order theory and the usefulness of the bandwidth selection method.

Nonparametric estimation with aggregated data

Linton, Oliver; Whang, Yoon-Jae
Fonte: London School of Economics and Political Science Research Publicador: London School of Economics and Political Science Research
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em /04/2002 Português
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We introduce a kernel-based estimator of the density function and regression function for data that have been grouped into family totals. We allow for a common intrafamily component but require that observations from different families be independent. We establish consistency and asymptotic normality for our procedures. As usual, the rates of convergence can be very slow depending on the behavior of the characteristic function at infinity. We investigate the practical performance of our method in a simple Monte Carlo experiment.

Supporting local data users in the UK academic community

Macdonald, Stuart; Martinez, Luis
Fonte: London School of Economics and Political Science Research Publicador: London School of Economics and Political Science Research
Tipo: Article; NonPeerReviewed Formato: application/pdf
Publicado em /07/2005 Português
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Data collection in the UK can be traced back to Roman times with the introduction of 5-yearly population censuses however it is only in recent history that the acquisition, distribution and analysis of quantitative data in digital format has been possible. 1967 saw the establishment of the SSRC Data Bank at the University of Essex. The 1970s and 1980s saw the emergence of ‘data laboratories’ within a number of UK tertiary education institutions. This evolution continued with the formation of Edinburgh University Data Library (1983) and Oxford Data Library (1985) and more recently the London School of Economics (LSE) Data Library and the LSE Research Laboratory Data Service. Based at tertiary education institutions these specialised libraries have developed independently to assist researchers and teachers in the use of quantitative data for analysis and research purposes. With Web technology and advances in telecommunications this role has continued to develop to include support for a whole range of digital data resources via National Data Centres. Thus in this digital age with increased IT literacy, technological exposure and expectancy the data librarian’s role is ever more confusing and difficult to identify. This paper will discuss the differing areas of expertise within the UK data libraries with particular reference to their relationship with National Data Centres...

Improved regression calibration

Skrondal, Anders; Kuha, Jouni
Fonte: The Psychometric Society Publicador: The Psychometric Society
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em 18/10/2012 Português
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The likelihood for generalized linear models with covariate measurement error cannot in general be expressed in closed form which makes maximum likelihood estimation taxing. A popular alternative is regression calibration which is computationally efficient at the cost of inconsistent estimation. We propose an improved regression calibration approach, a general pseudo maximum likelihood estimation method based on a conveniently decomposed form of the likelihood. It is both consistent and computationally efficient, and produces point estimates and estimated standard errors which are practically identical to those obtained by maximum likelihood. Simulations suggest that improved regression calibration which is easy to implement in standard software, works well in a range of situations.

More than just talk: the framing of transactional sex and its implications for vulnerability to HIV in Lesotho, Madagascar and South Africa

Stoebenau, Kirsten; Nixon, Stephanie A.; Rubincam, Clara; Willan, Samantha; Zembe, Yanga Z.N.; Tsikoane, Tumelo; Tanga, Pius T.; Bello, Haruna M.; Caceres, Carlos F.; Townsend, Loraine; Rakotoarison, Paul G.; Razafintsalama, Violette
Fonte: BioMed Central Ltd. Publicador: BioMed Central Ltd.
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em /09/2011 Português
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Background 'Transactional sex' was regarded by the mid-1990s as an important determinant of HIV transmission, particularly in sub-Saharan Africa. Little attention has been paid to what the terms used to denote transactional sex suggest about how it is understood. This study provides a nuanced set of descriptions of the meaning of transactional sex in three settings. Furthermore, we discuss how discourses around transactional sex suggest linkages to processes of globalization and hold implications for vulnerability to HIV. Methods The analysis in this article is based on three case studies conducted as part of a multi-country research project that investigated linkages between economic globalization and HIV. In this analysis, we contextualize and contrast the 'talk' about transactional sex through the following research methods in three study sites: descriptions revealed through semi-structured interviews with garment workers in Lesotho; focus groups with young women and men in Antananarivo, Madagascar; and focus groups and in-depth interviews with young women and men in Mbekweni, South Africa. Results Participants' talk about transactional sex reveals two themes: (1) 'The politics of differentiation' reflects how participants used language to demarcate identities...

Does mass drug administration for the integrated treatment of neglected tropical diseases really work?: assessing evidence for the control of schistosomiasis and soil-transmitted helminths in Uganda

Parker, Melissa; Allen, Tim
Fonte: BioMed Central Ltd. Publicador: BioMed Central Ltd.
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em /01/2011 Português
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Background Less is known about mass drug administration [MDA] for neglected tropical diseases [NTDs] than is suggested by those so vigorously promoting expansion of the approach. This paper fills an important gap: it draws upon local level research to examine the roll out of treatment for two NTDs, schistosomiasis and soil-transmitted helminths, in Uganda. Methods Ethnographic research was undertaken over a period of four years between 2005-2009 in north-west and south-east Uganda. In addition to participant observation, survey data recording self-reported take-up of drugs for schistosomiasis, soil-transmitted helminths and, where relevant, lymphatic filariasis and onchocerciasis was collected from a random sample of at least 10% of households at study locations. Data recording the take-up of drugs in Ministry of Health registers for NTDs were analysed in the light of these ethnographic and social survey data. Results The comparative analysis of the take-up of drugs among adults revealed that although most long term residents have been offered treatment at least once since 2004, the actual take up of drugs for schistosomiasis and soil-transmitted helminths varies considerably from one district to another and often also within districts. The specific reasons why MDA succeeds in some locations and falters in others relates to local dynamics. Issues such as population movement across borders...

Conditional spatial policy dependence: theory and model specification

Neumayer, Eric; Plümper, Thomas
Fonte: Sage Publications Publicador: Sage Publications
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em /07/2012 Português
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The authors discuss how scholars can bring theories of spatial policy dependence and empirical model specifications closer in line so that the empirical analysis actually tests the theoretical predictions. Comprehensive theories of spatial policy dependence typically suggest that the jurisdictions receiving spatial stimuli systematically differ in their exposure to such signals as a function of the intensity of their interaction with other jurisdictions. Similarly, theories often predict that governments also differ in their responsiveness to any given spatial stimulus as a function of the institutional, political, economic, or social context in which they operate. In other words, theories typically postulate that spatial dependence is conditional on exposure and responsiveness, neither of which is accounted for in the standard empirical practice of estimating one single common coefficient for a row-standardized spatial lag variable. The authors show how scholars can adequately model both forms of heterogeneity with properly specified interaction effects models.

From design to practice: how can large-scale household surveys better represent the complexities of the social units under investigation?

Kriel, Antoinette; Randall, Sara; Coast, Ernestina; Risenga, Arthur; Nyambura, Melissa
Fonte: London School of Economics and Political Science Research Publicador: London School of Economics and Political Science Research
Tipo: Conference or Workshop Item; NonPeerReviewed Formato: application/pdf
Publicado em /07/2012 Português
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‘The household’ is most commonly used as unit of analysis in household surveys and as enumeration unit during census data collection. Relationships are mostly indicated with regards to ‘household head’ or ‘acting household head’. The way in which ‘the household’ is defined in these surveys has long been criticised by anthropologists and sociologists as unable to adequately capture the complexities of the social units within which people arrange themselves. However the problem often doesn’t simply lie with the definition but the assumptions made when designing a questionnaire and taking the survey from the design phase into the implementation phase. The aim of this paper is to reflect on lessons learnt from a household financial well-being survey with regards to defining ‘the household’ and operationalising the definition in a heterogeneous, complex society such as South Africa. In a follow-up study group interviews were conducted with fieldworkers who administered the survey, and willing respondents were re-interviewed, collecting qualitative information about those with familial and/or financial links. It was found that: 1. There was already confusion at the survey design stage as to exactly what the unit of analysis is. 2. This confusion translated into lack of clarity in terms of operationalising the working definition given to fieldworkers. 3. Fieldworkers therefore reverted back to what they know...

Sofa surfers and shed dwellers: new living arrangements and household surveys in the UK and France

Coast, Ernestina; Randall, Sara; Fanghanel, Alex; Lelievre, Eva; Ba-Gning, Sadio
Fonte: London School of Economics and Political Science Research Publicador: London School of Economics and Political Science Research
Tipo: Conference or Workshop Item; NonPeerReviewed Formato: application/pdf
Publicado em /06/2012 Português
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Data collection practicalities and the need for meaningful data analysis require a social unit to be defined. The ‘household’ is almost universally used as this unit of survey enumeration. Despite apparent harmonisation, European countries have different interpretations of the definition of private household and there is a clear lack of harmonisation both between surveys and countries. This study aims understand the implications of harmonizing definitions of the ‘household’ for survey data to represent the realities of new and emergent living arrangements in Europe. We explore which new forms of living arrangements and households are captured and / or represented in household surveys and censuses in the UK and France. We use 2 research: in-depth semi-structured interviews with informants involved in the design and production of household surveys and censuses; and, case study households (n=60) in the UK and France, producing qualitative data on living arrangements. We find considerable variation in the extent to which understanding of household meshes with data collected. We identify population sub-groups that are likely to be poorly captured and represented by household surveys, including: people who live temporarily, often as a result of a critical change (eg:divorce)...

Mapping intergenerational care across households in the UK: analysing proximity, propinquity and resources in the "tacit intergenerational contract"

Fanghanel, Alex; Coast, Ernestina; Randall, Sara
Fonte: London School of Economics and Political Science Research Publicador: London School of Economics and Political Science Research
Tipo: Conference or Workshop Item; NonPeerReviewed Formato: application/pdf
Publicado em /06/2012 Português
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Intergenerational exchanges of care form the backbone of informal care arrangements in the UK. Against a background of cuts in public spending and an increasingly ageing population, the centrality of familial or kinship care, in the provision of everyday or practical intergenerational care (including providing housing, personal care, doing the shopping, providing childcare etc) is an ever more pressing question for policy-makers and ageing professionals. At present, flows of intergenerational care are difficult to capture precisely in surveys enumerated at the household level. In 2011 in the UK, the household was defined as‘one person living alone or a group of people (not necessarily related) living at the same address, who share cooking facilities and share a living room or a sitting room or a dining area’. Within this definition of the household, recognition of transfers of care which transcend the household are lacking. This has implications for recognising the financial, residential and temporal (amongst others) obligations which might tie households together and impact in a very real way on the day-to-day well-being of people at a societal level. Drawing on data gathered from interviews with policy makers and ageing specialists as well as from 36 purposively-sampled household interviews...

Book review: models as maps: the search for better explanations of political phenomena

Lauderdale, Benjamin E.
Fonte: Blog post from London School of Economics & Political Science Publicador: Blog post from London School of Economics & Political Science
Tipo: Website; NonPeerReviewed Formato: application/pdf
Publicado em 29/06/2012 Português
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A Model Discipline continues the long-running debate on the role of formal, mathematical models in political science and whether purely theoretical work should be published in top journals. Benjamin Lauderdale finds the larger points in the book compelling despite disagreeing with its arguments on what should actually be demanded of theoretical models.

‘The frightful inadequacy of most of the statistics’: a critique of Collier and Hoeffler on causes of civil war

Nathan, Laurie
Fonte: Crisis States Research Centre, London School of Economics and Political Science Publicador: Crisis States Research Centre, London School of Economics and Political Science
Tipo: Monograph; NonPeerReviewed Formato: application/pdf
Publicado em /09/2005 Português
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Over the past five years numerous cross-national statistical studies have been conducted on the causes of civil war. The most influential studies have been those by Paul Collier and Anke Hoeffler.Their work has been widely cited in international reports on security and stability. This paper offers a critique of their work, arguing that their research is filled with empirical, methodological and theoretical problems that lead to unreliable results and unjustified conclusions. Their most prominent finding - that dependence on natural resources heightens a country's risk of war because it affords rebels an opportunity for extortion - is not based on any evidence of rebel behaviour; it is an inference drawn from a correlation between the onset of civil war and the ratio of primary commodity exports to GDP. To borrow a felicitous phrase from Keynes, the Collier and Hoeffler model suffers from 'a frightful inadequacy of most of the statistics'.

The quandaries of coding and ranking: evaluating poor state performance indexes

Gutiérrez Sanín, Francisco
Fonte: Crisis States Research Centre, London School of Economics and Political Science Publicador: Crisis States Research Centre, London School of Economics and Political Science
Tipo: Monograph; NonPeerReviewed Formato: application/pdf
Publicado em /11/2009 Português
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How do we effectively measure poor state performance (PSP)? Determining fragile and poor performing states is an important but difficult task. This paper discusses and evaluates definitions and indexes of PSP. The author suggests that most of these exhibit poor conceptual definition, vast conceptual dispersion and confusion between causes and definitions. Moreover, they contain an intrinsic ambiguity and a lack of awareness of the problem of order. By undertaking a detailed analysis of methods of coding and ranking countries according to poor state performance, the author concludes that such indexes can only provide a useful resource for researchers if their assumptions are carefully discussed and if they can express critical aspects of the concept which they seek to codify. This paper identifies the difficulties inherent in classifying and ranking 'good' and 'bad' state performance using PSP indexes and databases. PSP models should complement sound qualitative and historical analysis to inform policy and research but, this research argues, they can only fulfill this task once they are critically assessed. Of the foremost challenges affecting the usefulness and accuracy of PSP databases, the author highlights hidden assumptions (revealed through detailed analysis of the 'numeraire' - a standard by which values are measured)...

Force and ambiguity: evaluating sources for cross-national research – the case of military interventions

Gutiérrez Sanín, Francisco; González Peña, Andrea
Fonte: Crisis States Research Centre, London School of Economics and Political Science Publicador: Crisis States Research Centre, London School of Economics and Political Science
Tipo: Monograph; NonPeerReviewed Formato: application/pdf
Publicado em /06/2009 Português
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This paper discusses the analytical problems associated with the increasing use of numerical databases in quantitative cross-national research. The authors highlight the need for a better understanding of the way these databases are constructed and their inherent ambiguities and they examine the existing critical literature. The paper makes a case study of data on military interventions and analyses the problems of classification that the authors identified in several well-known databases. The paper concludes that more attention should be given to modelling uncertainty rather than attempting to achieve clear-cut precision.

The explicit solution to a sequential switching problem with non-smooth data

Johnson, Timothy C.; Zervos, Mihail
Fonte: Taylor & Francis Publicador: Taylor & Francis
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em /02/2010 Português
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We consider the problem faced by a decision maker who can switch between two random payoff flows. Each of these payoff flows is an additive functional of a general 1D Ito diffusion. There are no bounds on the number or on the frequency of the times at which the decision maker can switch, but each switching incurs a cost, which may depend on the underlying diffusion. The objective of the decision maker is to select a sequence of switching times that maximizes the associated expected discounted payoff flow. In this context, we develop and study a model in the presence of assumptions that involve minimal smoothness requirements from the running payoff and switching cost functions, but which guarantee that the optimal strategies have relatively simple forms. In particular, we derive a complete and explicit characterization of the decision maker's optimal tactics, which can take qualitatively different forms, depending on the problem data.

Estimating linear dependence between nonstationary time series using the locally stationary wavelet model

Sanderson, Jean; Fryzlewicz, Piotr; Jones, M. W.
Fonte: Oxford University Press Publicador: Oxford University Press
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em /06/2010 Português
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Large volumes of neuroscience data comprise multiple, nonstationary electrophysiological or neuroimaging time series recorded from different brain regions. Accurately estimating the dependence between such neural time series is critical, since changes in the dependence structure are presumed to reflect functional interactions between neuronal populations. We propose a new dependence measure, derived from a bivariate locally stationary wavelet time series model. Since wavelets are localized in both time and scale, this approach leads to a natural, local and multi-scale estimate of nonstationary dependence. Our methodology is illustrated by application to a simulated example, and to electrophysiological data relating to interactions between the rat hippocampus and prefrontal cortex during working memory and decision making.