A likelihood ratio test for bimodality in two-component mixtures with application to regional income distribution in the EU

We propose a parametric test for bimodality based on the likelihood principle by using two-component mixtures. The test uses explicit characterizations of the modal structure of such mixtures in terms of their parameters. Examples include the univariate and multivariate normal distributions and the von Mises distribution. We present the asymptotic distribution of the proposed test and analyze its finite sample performance in a simulation study. To illustrate our method, we use mixtures to investigate the modal structure of the cross-sectional distribution of per capita log GDP across EU regions from 1977 to 1993. Although these mixtures clearly have two components over the whole time period, the resulting distributions evolve from bimodality toward unimodality at the end of the 1970s.     

A Model for Setting Performance Objectives for Salmonella in the Broiler Supply Chain

A stochastic model for setting performance objectives for Salmonella in the broiler supply chain was developed. The goal of this study was to develop a model by which performance objectives for Salmonella prevalence at various points in the production chain can be determined, based on a preset final performance objective at the end of the processing line. The transmission of Salmonella through the broiler production chain was modeled. The prevalence at flock level was calculated from the measured prevalence at sample level. The transmission model is based on data on the occurrence of Salmonella collected in the Dutch broiler production chain during several years. The developed model can be used by policymakers and industry to determine economically and politically acceptable performance objectives for various points of the production chain and to draw conclusions about which interventions are most appropriate.     

Modeling Logistic Performance in Quantitative Microbial Risk Assessment

In quantitative microbial risk assessment (QMRA), food safety in the food chain is modeled and simulated. In general, prevalences, concentrations, and numbers of microorganisms in media are investigated in the different steps from farm to fork. The underlying rates and conditions (such as storage times, temperatures, gas conditions, and their distributions) are determined. However, the logistic chain with its queues (storages, shelves) and mechanisms for ordering products is usually not taken into account. As a consequence, storage times—mutually dependent in successive steps in the chain—cannot be described adequately. This may have a great impact on the tails of risk distributions. Because food safety risks are generally very small, it is crucial to model the tails of (underlying) distributions as accurately as possible. Logistic performance can be modeled by describing the underlying planning and scheduling mechanisms in discrete-event modeling. This is common practice in operations research, specifically in supply chain management. In this article, we present the application of discrete-event modeling in the context of a QMRA for  Listeria monocytogenes  in fresh-cut iceberg lettuce. We show the potential value of discrete-event modeling in QMRA by calculating logistic interventions (modifications in the logistic chain) and determining their significance with respect to food safety.     

Testing for lack of fit in inverse regression—with applications to biophotonic imaging

Summary.  We propose two test statistics for use in inverse regression problems Y = K θ + ɛ , where K is a given linear operator which cannot be continuously inverted. Thus, only noisy, indirect observations Y for the function θ are available. Both test statistics have a counterpart in classical hypothesis testing, where they are called the order selection test and the data-driven Neyman smooth test. We also introduce two model selection criteria which extend the classical Akaike information criterion and Bayes information criterion to inverse regression problems. In a simulation study we show that the inverse order selection and Neyman smooth tests outperform their direct counterparts in many cases. The theory is motivated by data arising in confocal fluorescence microscopy. Here, images are observed with blurring, modelled as convolution, and stochastic error at subsequent times. The aim is then to reduce the signal-to-noise ratio by averaging over the distinct images. In this context it is relevant to decide whether the images are still equal, or have changed by outside influences such as moving of the object table.     

Estimation of a quadratic regression functional using the sinc kernel

We use the sinc kernel to construct an estimator for the integrated squared regression function. Asymptotic normality of the estimator at different rates is established, depending on whether the regression function vanishes or not.     

Testing for intercept‐scale switch in linear autoregression

Autoregressive models with switching regime are a frequently used class of nonlinear time series models, which are popular in finance, engineering, and other fields. We consider linear switching autoregressions in which the intercept and variance possibly switch simultaneously, while the autoregressive parameters are structural and hence the same in all states, and we propose quasi‐likelihood‐based tests for a regime switch in this class of models. Our motivation is from financial time series, where one expects states with high volatility and low mean together with states with low volatility and higher mean. We investigate the performance of our tests in a simulation study, and give an application to a series of IBM monthly stock returns. The Canadian Journal of Statistics 40: 427–446; 2012 © 2012 Statistical Society of Canada     

Shifting the refugee narrative? An automated frame analysis of Europe’s 2015 refugee crisis

In 2015, Europe faced the arrival of over 1.25 million refugees fleeing from war-affected countries. The public mainly learned about this issue through domestic media. Through the use of computer-assisted content analysis, this study identifies the most dominant frames employed in the coverage of refugee and asylum issues between January 2015 and January 2016 in six Austrian newspapers (N?=?10,606), particularly focusing on potential differences between quality and tabloid media, and on frame variations over time. The findings reveal that, apart from administrative aspects of coping with the arrivals, established narratives of security threat and economisation are most prominent. Humanitarianism frames and background information on the refugees’ situation are provided to a lesser extent. During the most intense phases of the crisis, the framing patterns of tabloid and quality media become highly similar. Media coverage broadens to multiple prominent frames as issue salience sharply increases, and then ‘crystallises’ into a more narrow set. In sum, the results confirm a predominance of stereotyped interpretations of refugee and asylum issues, and thus persisting journalistic routines in both, tabloid and quality media, even in times of a major political and humanitarian crisis.     

The provision of complementary pensions: Objectives, forms and constraints

In all former centrally planned economies, the question of how to restructure old-age income provisions and open the way to non-governmental, complementary pension schemes is being posed. This paper deals with four main areas of that problem. First, the various objectives of public and complementary schemes are discussed. The paper argues that without a broad consensus among the major interested parties there is a considerable danger that envisaged objectives will not be achieved. The second section reviews the main forms of complementary pension scheme and discusses the central characteristics of occupational and personal schemes. The third section addresses two critical policy areas: the kind of regulations that may be required in order to enforce the social and economic objectives; and the likely social and economic implications. On the basis of experience in OECD countries and the specific situation in countries in transition, the final section offers some tentative conclusions for Czechoslovakia, the main one being that during the initial phase of economic transition preference should be given to a simple defined contribution plan. Such a complementary scheme would be consistent with the lack of developed financial markets and the privatization plan of the government and require neither a great number of highly trained accountants and actuaries nor the comprehensive set of regulations a defined benefit plan is likely to dictate.     

Testing for two states in a hidden Markov model

The authors consider hidden Markov models (HMMs) whose latent process has m ≥ 2 states and whose state‐dependent distributions arise from a general one‐parameter family. They propose a test of the hypothesis m = 2. Their procedure is an extension to HMMs of the modified likelihood ratio statistic proposed by Chen, Chen & Kalbfleisch (2004) for testing two states in a finite mixture. The authors determine the asymptotic distribution of their test under the hypothesis m = 2 and investigate its finite‐sample properties in a simulation study. Their test is based on inference for the marginal mixture distribution of the HMM. In order to illustrate the additional difficulties due to the dependence structure of the HMM, they show how to test general regular hypotheses on the marginal mixture of HMMs via a quasi‐modified likelihood ratio. They also discuss two applications.     

The ABCs of nonfinancial defined contribution (NDC) schemes

Nonfinancial defined contribution (NDC) pension schemes have been successfully implemented since the mid‐1990s in a number of European countries such as Italy, Latvia, Norway, Poland and Sweden. The NDC approach features the lifelong contribution–benefit link of a financial defined contribution (FDC) personal account scheme, but is based on the pay‐as‐you‐go (PAYG) format. At its start out, the PAYG commitments of the preceding defined benefit (DB) system are converted into individual personal accounts, allowing for a smooth transition from the DB to the DC format, while avoiding the very high transition costs inherent in a move from a traditional PAYG DB scheme to a fully funded FDC scheme. The NDC approach implemented by the rule book is able to manage the economic and demographic risks inherent to a pension scheme and, by design, creates financial sustainability. As in any pension scheme, the linchpin between financial stability and adequacy is the retirement age; in the NDC approach the individual retirement age above the minimum age is by design self‐selected and by incentives should increase the effective retirement age in line with population ageing. As a systemic reform approach NDC has become a strong competitor to piecemeal parametric reforms of traditional nonfinancial DB (NDB) schemes. While frequent, these reforms are far from transparent and usually too timid and too late to create financial sustainability while providing adequate pensions for the average contributor. This article offers a largely non‐technical introduction to NDC schemes, their basic elements and advantages over NDB schemes, the key technical frontiers of the approach, and the experiences of NDC countries.