Finding disjoint paths on edge-colored graphs: more tractability results

The problem of finding the maximum number of vertex-disjoint uni-color paths in an edge-colored graph (called MaxCDP) has been recently introduced in literature, motivated by applications in social network analysis. In this paper we investigate how the complexity of the problem depends on graph parameters (namely the number of vertices to remove to make the graph a collection of disjoint paths and the size of the vertex cover of the graph), which makes sense since graphs in social networks are not random and have structure. The problem was known to be hard to approximate in polynomial time and not fixed-parameter tractable (FPT) for the natural parameter. Here, we show that it is still hard to approximate, even in FPT-time. Finally, we introduce a new variant of the problem, called MaxCDDP, whose goal is to find the maximum number of vertex-disjoint and color-disjoint uni-color paths. We extend some of the results of MaxCDP to this new variant, and we prove that unlike MaxCDP, MaxCDDP is already hard on graphs at distance two from disjoint paths.     

Themed section: the person-centred turn in welfare policies: bad wine in new bottles or a true social innovation?

This themed section is aimed at evaluating different personalised policies and at drawing a clear map of opportunities and challenges for future implementations. All the essays are based on evaluative researches and on original case studies. They concern different policies: the Australian National Disability Scheme (NDIS) a first serious venture into personalised funding; personalisation in the management of offenders in probation services within the English criminal justice system; social care services for young disabled people attempting to personalise their transition from childhood into adulthood (in Redbridge, UK); health personal plans for disabled people (in Sardinia, Italy). These case studies address the question of how transferable the concept of personalisation is from the social care sector to other and outline different methodologies for developing and evaluating person-centred policies. Last but not least they reflect on a bundle of issues which seem to emerge autonomously from such different case studies. We can sum up their results affirming that personalisation is not an individual consumer-client technology, simply confronted with a single market context and new professionals. It has to be steered within an appropriate context, including new type of professionals, users' led associations and a new governance's architecture. If the public role has to shape freedom and control, helping people to exercise choice in a collectively responsible way and, consequently, to participate in creating public goods, then the person-centred turn will have to confront, at least, some emergent issues, which in turn need specific forms of governance.     

Labour Supply: Which Theory? A Critical Empirical Assessment

ABSTRACT The aim of this paper is to test econometrically a number of models of labour supply which fall within the neoclassical and Keynesian theories, in an attempt to obtain indications of validation of the theories themselves. The econometric assessment, carried out with a cohort approach to labour supply, shows that Italian female participation rates react well to the variables belonging to both the neoclassical versions of models — with the exception of the version regarding intertemporal choices — and the Keynesian ones. Both in terms of testing for the selection of alternative regression models, such as those for non-nested hypotheses and for selection of regressors, and of “internal” investigation within the estimated models, the results obtained are not without ambiguity. They therefore leave open the question as to which theory can explain labour supply in the most significant and appropriate way.     

Just-in-time in ATO vehicle manufacturing: The Minivan-Piaggio V.E. case study

The system adopted by Piaggio V.E. to run the production of 'Minivan' aims at conciliating the manufacturing philosophy 'just-in-time' JIT with the creation of a wide range of end-product codes. Some general assumptions for a JIT production, with small lot sizes, are described together with their implementation in the operationorganizing system adopted by Piaggio V.E. for the 'Minivan' assembly line. The strategy pursued by Piaggio V.E. for the Minivan focuses on the quality of the product and the level of service in the form of fast order cycle and a high number of options offered on catalogue. According to the logic of an ATO production system, the customer orders a customized product and the manufacturer does not keep any finished inventory, but aims at effective management of the information flows.     

Service and Life Quality: The Case of Palermo

The research aims at analysing the ``quality' of some services offered to the citizens by the Commune of Palermo. The data available were gathered thanks to a sampling survey carried out in October 1997. The sample is made up of 1008 residents in the city of Palermo and is proportionally stratified according to the quarter of residence. Information was gathered by means of a telephone questionnaire. The answering rate was rather high and a great interest in the subjects dealt was taken.The research wants to individuate the degree of efficiency of the Commune of Palermo, also at administrative level, with some questions concerning the municipal council, taking the expectations of the citizens of the city into account through an analytic survey of the indicators measuring the judgement of the citizen towards the main services. This result will be the starting point of an exhaustive analysis aiming at the individuation of the ``quality of life' in Palermo, which is tightly connected with the services offered.     

Handling co-dependence issues in resampling-based variable selection procedures: a simulation study

If a number of candidate variables are available, variable selection is a key task aiming to identify those candidates which influence the outcome of interest. Methods as backward elimination, forward selection, etc. are often implemented, despite their drawbacks. One of these drawbacks is the instability of their results with respect to small perturbations in the data. To handle this issue, resampling-based procedures have been introduced; using a resampling technique, e.g. bootstrap, these procedures generate several pseudo-samples that are used to compute the inclusion frequency of each variable, i.e. the proportion of pseudo-samples in which the variable is selected. Based on the inclusion frequencies, it is possible to discriminate between relevant and irrelevant variables. These procedures may fail in case of correlated variables. To deal with this issue, two procedures based on 2×2 tables of inclusion frequencies have been developed in the literature. In this paper we analyse the behaviours of these two procedures and the role of their tuning parameters in an extensive simulation study.     

Information theoretic results for circular distributions

The broad class of generalized von Mises (GvM) circular distributions has certain optimal properties with respect to information theoretic quantities. It is shown that, under constraints on the trigonometric moments, and using the Kullback–Leibler information as the measure, the closest circular distribution to any other is of the GvM form. The lower bounds for the Kullback–Leibler information in this situation are also provided. The same problem is also considered using a modified version of the Kullback–Leibler information. Finally, series expansions are given for the entropy and the normalizing constants of the GvM distribution.     

Shedding light on the aim of stock options: a literature review

Stock options (hereafter SOs) have been extensively investigated by the literature. The debate has been mainly grounded in the agency theory that has interpreted these tools as mechanisms to align the conflicting interests of managers and owners towards the shareholder value maximization. However, the latest empirical evidence suggests that SOs are often used by opportunistic managers to extract rents to the detriment of shareholders. In addition, literature identifies the perceived cost as a further theoretical lens to interpret the use of SOs. Despite the growing interest around the topic, the research is still fragmented and fails to present a comprehensive picture on the factors that affect the aim of SOs. Our literature review attempts to fill this gap by providing a systematization of the studies on the topic. The paper concludes by presenting the theoretical and practical implications of the study and suggesting directions for future research.     

Analysing Space-Time Accessibility Towards the Implementation of the Light Rail System: The Case Study of Brescia

This paper proposes a methodology for investigation of the space–time relations of accessibility to public services and collective mobility. The paper assesses the space–time efficiency of local public transport facilities and makes an accessibility analysis as a baseline for evaluating future changes. It explains the potential for improvement and the effects on planning paradigms. Public transport accessibility greatly changes during day and night time so they should be assessed through multi-scaled and diachronic maps as a contribution to the timetable plan and overall planning strategies. The case study of Brescia, Italy is used to test the methodology. The new light rail system of Brescia entered into operation in 2013 and could change the entire form of urban mobility.     

The role of passing network indicators in modeling football outcomes: an application using Bayesian hierarchical models

AStA Advances in Statistical Analysis - Passes are undoubtedly the more frequent events in football and other team sports. Passing networks and their structural features can be useful to evaluate...