Discussion of “On simulation and properties of the stable law” by L. Devroye and L. James

We contribute to the discussion of the paper by Devroye and James, by reviewing some of the most meaningful results that relate the unilateral stable distribution with the asymptotic behavior of the so-called Ewens-Pitman sampling model. Our focus is then on how these results have been exploited in the context of Bayesian nonparametric inference for species sampling problems.     

Estimating unobservable signal by Markovian noise induction

A sub threshold signal is transmitted through a channel and may be detected when some noise - with known structure and proportional to some level - is added to the data. There is an optimal noise level, called of stochastic resonance, that corresponds to the minimum variance of the estimators in the problem of recovering unobservable signals. For several noise structures it has been shown the evidence of stochastic resonance effect. Here we study the case when the noise is a Markovian process. We propose consistent estimators of the sub threshold signal and we solve further a problem of hypotheses testing. We also discuss evidence of stochastic resonance for both estimation and hypotheses testing problems via examples.     

Purchasing performance management systems: an empirical investigation

This article aims at further developing the purchasing performance management systems (PPMSs) body of knowledge, assuming the wider perspective of the adoption process rather than key performance indicators (KPIs) only. In particular, the research questions are focused on understanding what are the most adopted indicators, what are the key elements characterising the implementation process and what are the differences among different organisational levels and different purchasing categories. The literature provides a framework for classifying purchasing KPIs, identifying the implementation process and the PPMS architecture, thus supporting the empirical research protocol. Nine case studies of large multinationals belonging to different industries are conducted. Empirical evidence shows that companies are still adopting mainly an external perspective, by focusing on performance measurement efforts on suppliers. Widely adopted indicators mainly measure cost, time and quality. However, the purchasing department has acquired an important role within the organisation and new performance indicators have been created; flexibility, innovation and sustainability are becoming increasingly important.     

Recoverable robust timetabling for single delay: Complexity and polynomial algorithms for special cases

In this paper, we study the problem of planning a timetable for passenger trains considering that possible delays might occur due to unpredictable circumstances. If a delay occurs, a timetable could not be able to manage it unless some extra time has been scheduled in advance. Delays might be managed in several ways and the usual objective function considered for such purpose is the minimization of the overall waiting time caused to passengers. We analyze the timetable planning problem in terms of the recoverable robustness model, where a timetable is said to be recoverable robust if it is able to absorb small delays by possibly applying given limited recovery capabilities. The quality of a robust timetable is measured by the price of robustness that is the ratio between the cost of the recoverable robust timetable and that of a non-robust optimal one.     

Measuring Change Over Time in Socio-economic Deprivation and Health in an Urban Context: The Case Study of Genoa

Poverty and disability are interrelated, but data that can disentangle to what extent one causes the other and vice versa is not available. However, data from Vietnam allows us to examine this interrelationship in a way not done previously. Using small area estimation techniques, we uncover three findings not yet found in the literature. First, disability prevalence rates vary significantly within a country even at the district level. Second, the poverty gap between people with and without disabilities also varies at the district level. And most importantly, the size of that gap lessens based on district characteristics that can be affected by policy. Districts with better health care and infrastructure, such as road and health services, show less of a link between disability and poverty, supporting the hypothesis that improvements in infrastructure and rehabilitation service can lessen the impact of disability on families with disabled members.     

Diversity as width

It is argued that if a finite partially ordered population is given, and incomparability is taken as the relevant type of dissimilarity, then diversity comparisons between subpopulations may be conveniently based on widths namely on the maximum number of pairwise incomparable units they include. We introduce two width-based rankings. The first one is the plain width-ranking of subposets as induced by width computation. The second one is the undominated width-ranking of subposets namely the ranking induced by the sizes of undominated subposets. Simple axiomatic characterizations of the foregoing rankings are provided.