Multiple change points detection and clustering in dynamic networks

The increasing amount of data stored in the form of dynamic interactions between actors necessitates the use of methodologies to automatically extract relevant information. The interactions can be represented by dynamic networks in which most existing methods look for clusters of vertices to summarize the data. In this paper, a new framework is proposed in order to cluster the vertices while detecting change points in the intensities of the interactions. These change points are key in the understanding of the temporal interactions. The model used involves non-homogeneous Poisson point processes with cluster-dependent piecewise constant intensity functions and common discontinuity points. A variational expectation maximization algorithm is derived for inference. We show that the pruned exact linear time method, originally developed for change points detection in univariate time series, can be considered for the maximization step. This allows the detection of both the number of change points and their location. Experiments on artificial and real datasets are carried out, and the proposed approach is compared with related methods.     

Wild adaptive trimming for robust estimation and cluster analysis

Trimming principles play an important role in robust statistics. However, their use for clustering typically requires some preliminary information about the contamination rate and the number of groups. We suggest a fresh approach to trimming that does not rely on this knowledge and that proves to be particularly suited for solving problems in robust cluster analysis. Our approach replaces the original K‐population (robust) estimation problem with K distinct one‐population steps, which take advantage of the good breakdown properties of trimmed estimators when the trimming level exceeds the usual bound of 0.5. In this setting, we prove that exact affine equivariance is lost on one hand but, on the other hand, an arbitrarily high breakdown point can be achieved by “anchoring” the robust estimator. We also support the use of adaptive trimming schemes, in order to infer the contamination rate from the data. A further bonus of our methodology is its ability to provide a reliable choice of the usually unknown number of groups.     

An information theoretic approach to post randomization methods under differential privacy

Statistics and Computing - Post randomization methods are among the most popular disclosure limitation techniques for both categorical and continuous data. In the categorical case, given a...     

Costs and Financing of Maritime Education and Training in Europe: Analysis and Policy Implications

The paper reports some findings of an extensive European research project carried out on costs and funds of MET (maritime education and training) systems. The need to improve the quality of the European MET systems is a relevant political and scientific issue which strongly impacts the competitiveness of the shipping sector in Europe. However, MET is quite an expensive ET system since it requires high investments and incurs in high running costs. The situation is also acerbated by the decreasing number of students at MET institutions. There is then the need of having a closer look at the financial aspects of MET so as to come up with some policy recommendations for improving the current situation in terms of optimal use of resources. In the paper a questionnaire-based methodology is employed aiming at identifying and analyzing different cost and funds structures of MET institutions in Europe (cost models). Then, by considering some policy-sensitive variables of the cost models, some policy recommendations are drawn up to improve the efficiency of current systems. They basically refer to the need to concentrate and integrate resources in order to exploit some degree of economies of scale, on top of achieving some economies of scope and pursuing quality in MET. Finally, further lines of research are indicated.     

A strong paradox of multiple elections

We consider a stronger version of the paradox of multiple elections and show that it is possible that not only the winning combination of propositions, but also all the combinations sufficiently close to it, receive zero votes. Received: 8 April 1997/Accepted: 18 April 1997     

A qualitative look at child care selection among rural welfare-to-work participants

The welfare reforms of 1996 changed the administration of public assistance to children and families. One of the key provisions, requiring parents to join the workforce, resulted in an expanded need for child care. Prior research demonstrates that welfare recipients, particularly in rural areas, utilize informal child care arrangements. Further, recipients in rural communities face greater challenges due to a lack of transportation, geographic spread, and less access to services. This qualitative study examined the child care selection experiences of 33 welfare recipients in six rural Northern California counties. More families selected home-based than center-based child care. During their search processes, welfare recipients utilized both formal and informal routes to locate child care providers. Parents took advantage of their connections with the social service system, but also accessed their social networks for recommendations. Rural families also reported that their choices were constrained by the available programs, transportation, and by the quality of the programs they were able to access. Given the high rate of utilization of home-based arrangements among families in welfare-to-work programs, quality of care in such programs should be improved. Recommendations for increasing quality and access, as well as supports for welfare to work participants, are discussed.     

Strategic monitoring of port authorities activities: Proposal of a multi-dimensional digital dashboard

Abstract

The consequence of port evolution is that port authorities (PA) around the world are modifying their nature and their role, acquiring more and more an active role in the governance of logistic systems and are often adopting managerial and entrepreneurial behaviours. This new role of PA requires the adoption of a complex approach to monitoring the performance of the single stakeholders and of the whole port. Existing studies on port performance consider only specific indicators of port performance such as operational and financial efficiency neglecting aspects like customer satisfaction, port security and port sustainability. This paper tries to fill this literature gap: (i) outlining an integrated multi-dimensional dashboard to monitor port performance in a strategic perspective; (ii) analysing the role of digital technology to support the PA in the implementation of the monitoring dashboard; (iii) defining the evolutionary stages of tools implementation in the strategic monitoring of PAs.     

Market research with the aid of a smartphone application – a case study

We discuss using the presumed ‘wisdom of the crowd’ to reduce the bullwhip effect in supply chains by enhancing the accuracy of demand forecast. Our case study describes a joint project of a leading European technology company (We chose RAGD as a pseudonym for the company throughout the study.) and the University of Kassel on a smartphone application for end customers to gather early information for this producer’s forecast. Our results confirm the ‘wisdom of the crowd’ hypothesis: A group of experts, in our case technicians who install and maintain RAGD-products, is capable of anticipating market fluctuations six weeks in advance. This only holds true if the ‘crowd’ of technicians is large enough. Our business climate index outperforms the company forecast in the first six months, when on average 22 technicians took part per week. We discuss successes and limitations of the cooperation and provide recommendations for similar projects.     

LEGAL STANDARDS,ENFORCEMENT, AND CORRUPTION

Stricter laws require more incisive and costlier enforcement. Because enforcement activity depends both on available tax revenue and the honesty of officials, the optimal legal standard of a benevolent government is increasing in per capita income and decreasing in officials' corruption. In contrast to the “tollbooth view” of regulation, the standard chosen by a self‐interested government is a non‐monotonic function of officials' corruption, and can be either lower or higher than that chosen by a benevolent regulator. International evidence on environmental regulation shows that standards correlate positively with per‐capita income, and negatively with corruption, consistent with the model's predictions for benevolent governments. (JEL: D73, K42, L51)