Stuart Barber

Stuart Barber
University of Leeds · Department of Statistics

PhD Statistics

About

45
Publications
11,496
Reads
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610
Citations
Introduction
Additional affiliations
August 2009 - present
University of Leeds
Position
  • Professor (Associate)
July 2003 - July 2009
University of Leeds
Position
  • Lecturer
July 1999 - June 2003
University of Bristol
Position
  • PostDoc Position

Publications

Publications (45)
Chapter
Finite mixture models are fitted to spherical data. Kent distributions are used for the components of the mixture because they allow considerable flexibility. Previous work on such mixtures has used an approximate maximum likelihood estimator for the parameters of a single component. However, the approximation causes problems when using the EM algo...
Preprint
Full-text available
Finite mixture models are fitted to spherical data. Kent distributions are used for the components of the mixture because they allow considerable flexibility. Previous work on such mixtures has used an approximate maximum likelihood estimator for the parameters of a single component. However, the approximation causes problems when using the EM algo...
Article
Many spatial statistics methods require neighbourhood structures such as the one determined by a Voronoi tessellation, so understanding statistical properties of Voronoi cells is crucial. While distributions of cell properties when data locations follow an unbounded homogeneous Poisson process have been studied, little attention has been given to h...
Article
In forecasting, we often require interval forecasts instead of just a specific point forecast. To track streaming data effectively, this interval forecast should reliably cover the observed data and yet be as narrow as possible. To achieve this, we propose two methods based on regression trees: one ensemble method and one method based on a single t...
Article
Many methods for modelling functions over high-dimensional spaces assume global smoothness properties; such assumptions are often violated in practice. We introduce a method for modelling functions that display heterogeneity or contain discontinuities. The heterogeneity is dealt with by using a combination of Voronoi tessellation, to partition the...
Article
Eicosanoids comprise a diverse group of bioactive lipids which orchestrate inflammation, immunity and tissue homeostasis, and whose dysregulation has been implicated in carcinogenesis. Among the various eicosanoid metabolic pathways, studies of their role in endometrial cancer (EC) have very much been confined to the COX‐2 pathway. This study aimed...
Article
Wavelet-transformed variables can have better classification performance for panel data than using variables on their original scale. Examples are provided showing the types of data where using a wavelet-based representation is likely to improve classification accuracy. Results show that in most cases wavelet-transformed data have better or similar...
Article
Many methods for modelling spatial processes assume global smoothness properties; such assumptions are often violated in practice. We introduce a method for modelling spatial processes that display heterogeneity or contain discontinuities. The problem of non-stationarity is dealt with by using a combination of Voronoi tessellation to partition the...
Article
We introduce a new method to test efficiently for cospeciation in tritrophic systems. Our method utilises an analogy with electrical circuit theory to reduce higher order systems into bitrophic data sets that retain the information of the original system. We use a sophisticated permutation scheme that weights interactions between two trophic layers...
Chapter
We focus our analysis on the structural alignment of proteins from the trypsin family. Calculating basic summary statistics on the resulting aligned distance matrices revealed an interesting result. We discovered a set of residues where the distance between these specific residues and every other residue in each structure is highly conserved across...
Article
Full-text available
Selection bias is well known to affect surveys and epidemiological studies. There have been numerous methods proposed to reduce its effects, so many that researchers may be unclear which method is most suitable for their study; the wide choice may even deter some researchers, for fear of choosing a sub-optimal approach. We propose a straightforward...
Article
A general framework for regression modeling using localized frequency characteristics of explanatory variables is proposed. This novel framework can be used in any application where the aim is to model an evolving process sequentially based on multiple time series data. Furthermore, this framework allows time series to be transformed and combined t...
Article
One of the major problems in biology is related to protein folding. The folding process is known to depend on both the protein's sequence (1-D) and structure (3-D). Both these properties need to be considered when aligning two proteins; they are also influenced by the evolutionary distance between the proteins to be aligned. We propose a Bayesian m...
Article
Full-text available
Approximate Bayesian Computation (ABC) is a popular computational method for likelihood-free Bayesian inference. The term "likelihood-free" refers to problems where the likelihood is intractable to compute or estimate directly, but where it is possible to generate simulated data $X$ relatively easily given a candidate set of parameters $\theta$ sim...
Article
Full-text available
Studies into participation bias have examined participation trends, where it occurs, the factors affecting it, and methods to try to reduce it. However, some authors only discuss participation bias at the end of the study, some acknowledge it and apply a method to try to reduce it, while others ignore it or dismiss it as negligible. Issues of three...
Article
Full-text available
Abstract There is a need for a reliable statistical test which is appropriate for assessing cospeciation of more than two phylogenies. We have developed an algorithm using a permutation method that can be used to test for and infer tri-trophic evolutionary relationships of organisms given both their phylogenies and pairwise interactions. An overall...
Article
Full-text available
We develop a Bayesian model for the alignment of two point configurations under the full similarity transformations of rotation, translation and scaling. Other work in this area has concentrated on rigid body transformations, where scale information is preserved, motivated by problems involving molecular data; this is known as form analysis. We con...
Article
There is a considerable need to rationalize the membrane permeability and mechanism of transport for potential nutraceuticals. The aim of this investigation was to develop a theoretical permeability equation, based on a reported descriptive absorption model, enabling calculation of the transcellular component of absorption across Caco-2 monolayers....
Article
One of the key ingredients in drug discovery is the derivation of conceptual templates called pharmacophores. A pharmacophore model characterizes the physicochemical properties common to all active molecules, called ligands, bound to a particular protein receptor, together with their relative spatial arrangement. Motivated by this important applica...
Article
Full-text available
We survey existing methods of inference using the Kaplan-Meier estimator, focusing on testing H 0 :St = p for some chosen t and p . Performance of these methods is assessed by simulation. The problems these methods encounter are analysed and the reasons for these problems discussed.
Article
Full-text available
Amyotrophic lateral sclerosis (ALS) is an adult-onset neurodegenerative disease, characterized by progressive dysfunction and death of motor neurons. Although evidence for oxidative stress in ALS pathogenesis is well described, antioxidants have generally shown poor efficacy in animal models and human clinical trials. We have developed an in vitro...
Article
A typical microarray experiment attempts to ascertain which genes display differential expression in different samples. We model the data by using a two-component mixture model and develop an empirical Bayesian thresholding procedure, which was originally introduced for thresholding wavelet coefficients, as an alternative to the existing methods fo...
Article
The aim of industrial process control is to convert measurements, taken while the process is evolving, into parameters which can be used to control the process. To be of practical use this must all be computationally efficient allowing real-time feedback. Electrical tomography measurements have the potential to provide useful data without intruding...
Article
Wavelet shrinkage is an effective nonparametric regression technique, especially when the underlying curve has irregular features such as spikes or discontinuities. The basic idea is simple: take the discrete wavelet transform of data consisting of a signal corrupted by noise; shrink or remove the wavelet coefficients to remove the noise; then inve...
Article
Full-text available
This report details the results of extensive simulations carried out to compare the wavelet shrinkage methods proposed by Barber & Nason (2003) to a range of other existing wavelet shrinkage techniques.
Article
Full-text available
We extend the optimal symmetric group sequential tests of Eales & Jennison (1992) to the broader class of asymmetric designs. Two forms of asymmetry are considered, involving unequal type I and type II error rates and different emphases on expected sample sizes at the null and alternative hypotheses. We discuss the properties of our optimal designs...
Article
We use cumulants to derive Bayesian credible intervals for wavelet regression estimates. The first four cumulants of the posterior distribution of the estimates are expressed in terms of the observed data and integer powers of the mother wavelet functions. These powers are closely approximated by linear combinations of wavelet scaling functions at...
Article
Full-text available
Several authors have considered Bayesian approaches to wavelet shrinkage and thresholding. Relatively few of the resulting nonparametric curve estimates have associated uncertainty bands. We consider a simulation based approach to computing uncertainty bands based on the BayesThresh rule of Abramovich, Sapatinas & Silverman (1998).
Article
We describe existing tests and introduce two new tests concerning the value of a survival function. These tests may be used to construct a confidence interval for the survival probability at a given time or for a quantile of the survival distribution. Simulation studies show that error rates can differ substantially from their nominal values, parti...
Article
Full-text available
Barber & Jennison (2003) have proposed a method of evaluating optimal group sequential designs for clinical trials when the number of observations in each group is unknown. This enables the construction of flexible optimal designs. In order to construct such a test, a stochastic model must be specified for the size of each group. We consider severa...
Article
Full-text available
HPLC spectroscopy data can be used to determine the presence or absence of compounds in a sample. In a typical HPLC experiment, we have measurements f , that are taken on a grid of points x (which may be an irregular grid). We regard these measurements f as values f(xi) of a function at points x1, . . . , xn. When plotted, the data produce a trace...
Article
Full-text available
The aim of industrial process control is to convert measurements, taken while the process is evolving, into parameters which can be used to control the process. That is to monitor an active process and predict unacceptable or sub-optimal behaviour. To be of practical use this must all be computationally effi cient allowing real-time feedback. Elect...
Article
Full-text available
The aim of industrial process control is to convert measurements, taken while the process is evolving, into parameters which can be used to control the process. That is to monitor an active process and predict unacceptable or sub-optimal behaviour before it has occurred. To be of practical use this must all be computationally efficient allowing rea...
Article
A typical microarray experiment attempts to ascertain which genes display differential expres- sion between various different samples. Supposing we were testing just one gene with a large number of replicates, the conventional method to establish this would be some form of signifi- cance testing. However, experiments of this sort often involve look...
Article
Full-text available
This paper points out deficiencies in the methods that are used to judge the effectiveness of crime reduction interventions. A problem with using a Poisson model is that the variance of the number of crimes recorded, within an area in a period of time, is many times the mean rather than simply being equal to the mean number; that is there is overdi...

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