The turning arcs: a computationally efficient algorithm to simulate isotropic vector-valued Gaussian random fields on the d-sphere

Statistics and Computing - Random fields on the sphere play a fundamental role in the natural sciences. This paper presents a simulation algorithm parenthetical to the spectral turning bands method...     

Space-time estimation of a particle system model

Let X be a discrete time contact process (CP) on ?², as defined by Durrett and Levin (1994, Stochastic spatial models: a user's guide to ecological applications. Philosophical Transactions of the Royal Society of London Series B, 343, 329–350). We study the estimation of the model based on space-time evolution of X, that is, T + 1 successive observations of X on a finite subset S of sites. We consider the maximum marginal pseudo-likelihood (MPL) estimator and show that, when T→∞, this estimator is consistent and asymptotically normal for a non-vanishing supercritical CP. Numerical studies confirm these theoretical ones.     

Using Economic Freedom Indexes as Policy Indicators: An Intercontinental Example

We use time-series cross-section analysis to provide empirical validation for the existence of a specific American ethos and a specific European ethos with respect to economic policy. In our innovation, economic policy is proxied by “economic freedom” from the Fraser Institute database and constitutional “political institutions” are proxied by variables from the Database of Political Institutions (from the World Bank). Our results suggest that, once we control for political and institutional differences, the United States and Europe still pursue different economic policies.

Sensitivity analysis of the unconfoundedness assumption with an application to an evaluation of college choice effects on earnings

We evaluate the effects of college choice on earnings using Swedish register databases. This case study is used to motivate the introduction of a novel procedure to analyse the sensitivity of such an observational study to the assumption made that there are no unobserved confounders – variables affecting both college choice and earnings. This assumption is not testable without further information, and should be considered an approximation of reality. To perform a sensitivity analysis, we measure the departure from the unconfoundedness assumption with the correlation between college choice and earnings when conditioning on observed covariates. The use of a correlation as a measure of dependence allows us to propose a standardised procedure by advocating the use of a fixed value for the correlation, typically 1% or 5%, when checking the sensitivity of an evaluation study. A correlation coefficient is, moreover, intuitive to most empirical scientists, which makes the results of our sensitivity analysis easier to communicate than those of previously proposed methods. In our evaluation of the effects of college choice on earnings, the significantly positive effect obtained could not be questioned by a sensitivity analysis allowing for unobserved confounders inducing at most 5% correlation between college choice and earnings.     

Generalized Linear Factor Models: A New Local EM Estimation Algorithm

In this article, a general approach to latent variable models based on an underlying generalized linear model (GLM) with factor analysis observation process is introduced. We call these models Generalized Linear Factor Models (GLFM). The observations are produced from a general model framework that involves observed and latent variables that are assumed to be distributed in the exponential family. More specifically, we concentrate on situations where the observed variables are both discretely measured (e.g., binomial, Poisson) and continuously distributed (e.g., gamma). The common latent factors are assumed to be independent with a standard multivariate normal distribution. Practical details of training such models with a new local expectation-maximization (EM) algorithm, which can be considered as a generalized EM-type algorithm, are also discussed. In conjunction with an approximated version of the Fisher score algorithm (FSA), we show how to calculate maximum likelihood estimates of the model parameters, and to yield inferences about the unobservable path of the common factors. The methodology is illustrated by an extensive Monte Carlo simulation study and the results show promising performance.     

Experimentation order in factorial designs: new findings

Under some very reasonable hypotheses, it becomes evident that randomizing the run order of a factorial experiment does not always neutralize the effect of undesirable factors. Yet, these factors do have an influence on the response, depending on the order in which the experiments are conducted. On the other hand, changing the factor levels is many times costly; therefore it is not reasonable to leave to chance the number of changes necessary. For this reason, run orders that offer the minimum number of factor level changes and at the same time minimize the possible influence of undesirable factors on the experimentation have been sought. Sequences which are known to produce the desired properties in designs with 8 and 16 experiments can be found in the literature. In this paper, we provide the best possible sequences for designs with 32 experiments, as well as sequences that offer excellent properties for designs with 64 and 128 experiments. The method used to find them is based on a mixture of algorithmic searches and an augmentation of smaller designs.     

Measuring management quality in the factory

The last decade has seen a growing consensus that manufacturing matters. The factory as the producing unit is the core of the firm's manufacturing activities. However, even now, it is not agreed on or even fully understood what constitutes a well-managed factory. This article attempts to create a causal model of management quality in the plant, identifying key managerial levers for improving plant performance. The model is based on an integrated view of three core processes: supply chain, product and process development, and strategy deployment. We postulate that the joint performance of the three processes is determined by the quality with which they are managed. Management quality is operationalized as consisting of six types of action: delegation (or decentralization), integration (or coordination), measurement, employee participation, communication, and employee development.This management quality model has been applied to the design of the Top Usine 1995 Best Factory Award administered in cooperation with the French weekly L'Usine Nouvelle. Data collected from participating plants do substantiate our view that plant performance is substantially driven by management quality: the six management quality dimensions are shown to be statistically linked to performance improvement rates in the plant, and we provide further evidence of this link by detailing the case example of the award winner. Our survey also shows that supply management appears to be a common problem area for the factories participating in the Top Usine award, including the best ones.     

The use of economic appraisal in transportation analysis

This paper surveys the use of economic appraisal techniques in the field of transportation. After surveying the history of such approaches, a critical assessment is offered of the most recent contributions to the debate, centering on the 1977 Leitch Report. The limited room for manoeuvre in making local assessments is highlighted: national policy considerations are seen as frequently dominating the local choice. While most of the debate on the ‘inadequacies’ of cost-benefit have focussed on ‘intangible’ items, the author argues for a much closer look at the ‘hard’ data on the value of time-savings and accident costs. Some of the Leitch committee's proposals are found wanting in this respect. In the wider context, a plea is made for the use of common criteria for assessing projects throughout the entire transport sector. Only in this way can misallocation of resources be minimised.