Peter A W Lewis

Bio: Peter A W Lewis is an academic researcher. The author has contributed to research in topics: Statistician. The author has an hindex of 1, co-authored 1 publications receiving 1992 citations.

The statistical analysis of series of events

Abstract: Observations in the form of point events occurring in a continuum, space or time, arise in many fields of study. In writing this monograph on statistical techniques for dealing with such data, we have three objectives. First, we have tried to give a simple description, with numerical examples, of the main methods that have been proposed. We hope that by concentrating on the examples the applied statistician with a limited inclination for theory will find something of practical value in the monograph. Second, the monograph is intended as a survey, necessarily incomplete, of some of the problems in theoretical statistics that stem from this sort of data. A number of specialized subjects have, however, been dealt with only briefly, the main emphasis being placed on the problem of examining the structure of a series of events. Finally, we hope that the monograph will be of use to teachers and students of statistics, as illustrating applications of a range of tech niques in theoretical statistics. We are extremely grateful to the International Business Machines Corporation for providing programming assistance and a large amount of computer time. We wish to thank particularly Mr A."

Posterior predictive assessment of model fitness via realized discrepancies

Abstract: This paper considers Bayesian counterparts of the classical tests for good- ness of fit and their use in judging the fit of a single Bayesian model to the observed data. We focus on posterior predictive assessment, in a framework that also includes conditioning on auxiliary statistics. The Bayesian formulation facilitates the con- struction and calculation of a meaningful reference distribution not only for any (classical) statistic, but also for any parameter-dependent "statistic" or discrep- ancy. The latter allows us to propose the realized discrepancy assessment of model fitness, which directly measures the true discrepancy between data and the posited model, for any aspect of the model which we want to explore. The computation required for the realized discrepancy assessment is a straightforward byproduct of the posterior simulation used for the original Bayesian analysis. We illustrate with three applied examples. The first example, which serves mainly to motivate the work, illustrates the difficulty of classical tests in assessing the fitness of a Poisson model to a positron emission tomography image that is constrained to be nonnegative. The second and third examples illustrate the details of the posterior predictive approach in two problems: estimation in a model with inequality constraints on the parameters, and estimation in a mixture model. In all three examples, standard test statistics (either a χ 2 or a likelihood ratio) are not pivotal: the difficulty is not just how to compute the reference distribution for the test, but that in the classical framework no such distribution exists, independent of the unknown model parameters.

Spectra of some self-exciting and mutually exciting point processes

Abstract: SUMMARY In recent years methods of data analysis for point processes have received some attention, for example, by Cox & Lewis (1966) and Lewis (1964). In particular Bartlett (1963a,b) has introduced methods of analysis based on the point spectrum. Theoretical models are relatively sparse. In this paper the theoretical properties of a class of processes with particular reference to the point spectrum or corresponding covariance density functions are discussed. A particular result is a self-exciting process with the same second-order properties as a certain doubly stochastic process. These are not distinguishable by methods of data analysis based on these properties.

The Second-Order Analysis of Stationary Point Processes

Abstract: This paper provides a rigorous foundation for the second-order analysis of stationary point processes on general spaces. It illuminates the results of Bartlett on spatial point processes, and covers the point processes of stochastic geometry, including the line and hyperplane processes of Davidson and Krickeberg. The main tool is the decomposition of moment measures pioneered by Krickeberg and Vere-Jones. Finally some practical aspects of the analysis of point processes are discussed.

The Rotary Motor of Bacterial Flagella

Abstract: Flagellated bacteria, such as Escherichia coli, swim by rotating thin helical filaments, each driven at its base by a reversible rotary motor, powered by an ion flux. A motor is about 45 nm in diameter and is assembled from about 20 different kinds of parts. It develops maximum torque at stall but can spin several hundred Hz. Its direction of rotation is controlled by a sensory system that enables cells to accumulate in regions deemed more favorable. We know a great deal about motor structure, genetics, assembly, and function, but we do not really understand how it works. We need more crystal structures. All of this is reviewed, but the emphasis is on function.