Bounds for the Expected Time to Extinction and the Probability of Extinction in the Galton-Watson Process

Upper bounds for the expected time to extinction in the Galton-Watson process are obtained. We also found upper and lower bounds for the probability of extinction of this process. These bounds improve some bounds previously obtained by other authors.     

Negative Dependence in Sampling

Abstract. The strong Rayleigh property is a new and robust negative dependence property that implies negative association; in fact it implies conditional negative association closed under external fields (CNA+). Suppose that and are two families of 0‐1 random variables that satisfy the strong Rayleigh property and let . We show that {Z_i} conditioned on is also strongly Rayleigh; this turns out to be an easy consequence of the results on preservation of stability of polynomials of Borcea & Brändén (Invent. Math., 177, 2009, 521–569). This entails that a number of important π ps sampling algorithms, including Sampford sampling and Pareto sampling, are CNA+. As a consequence, statistics based on such samples automatically satisfy a version of the Central Limit Theorem for triangular arrays.     

Transnational mobility and rootedness: the upper middle classes in European cities

Some authors argue that ‘mobilities’ form the distinctive feature of late modern societies and represent a new social cleavage between cosmopolitan mobile élites and urban residents more rooted in their local neighbourhoods. One assumption in contemporary discourses of rootedness is that this new transnational or global society entails an ongoing process of uprooting individuals and a mainly mobile élite packing up and relocating. In this article, we draw on empirical comparative research to examine the patterns and dynamics of mobility and belonging across European borders among upper‐middle‐class managers in four cities – Paris, Madrid, Milan and Lyon. We suggest that these new urban upper‐middle‐class managers display flight responses, or ‘partial exit’ strategies, which operate at various levels to enable them to protect and control their interests while holding onto the reins of power in their local communities. Our study adopts a micro‐level perspective to explore individual experiences, strategies, motivations and values based on interviews with 480 managers in these cities.     

The worldwide maritime network of container shipping: spatial structure and regional dynamics

Port and maritime studies dealing with containerization have observed traffic concentration and dispersion throughout the world. Globalization, intermodal transportation, and technological revolutions in the shipping industry have resulted in both network extension and rationalization. However, lack of precise data on inter‐port relations prevent the application of wider network theories to global maritime container networks, which are often examined through case studies of specific firms or regions. In this article, we present an analysis of the global liner shipping network in 1996 and 2006, a period of rapid change in port hierarchies and liner service configurations. While we refer to literature on port system development, shipping networks, and port selection, the article is one of the only analyses of the properties of the global container shipping network. We analyse the relative position of ports in the global network through indicators of centrality. The results reveal a certain level of robustness in the global shipping network. While transhipment hub flows and gateway flows might slightly shift among nodes in the network, the network properties remain rather stable in terms of the main nodes polarizing the network and the overall structure of the system. In addition, mapping the changing centrality of ports confirms the impacts of global trade and logistics shifts on the port hierarchy and indicates that changes are predominantly geographic.     

WebStress: A web interface to explore a multidatabase bibliographic corpus on occupational stress

A bibliographic study on a multidisciplinary subject, such as occupational stress, requires a multidatabase query facility. Given this, we searched eight databases belonging to different fields (medicine, psychology, etc.) and from different countries. Thus, more than 26000 references on occupational stress were gathered. A bibliographic corpus of this sort is unusable because of the heterogeneous format of the records and the number of duplicate entries. Considering the limitations of commercial programs, we have developed a system, called WebStress, for reformatting the data and removing duplicates. The huge number of references and the research needs of updating and searching have necessitated the addition of several other functions to WebStress. Therefore WebStress comprises a web interface that makes it possible to search the corpus with advanced features (using clustering, a specialized thesaurus on stress and Boolean queries). In addition to the usual bibliographic queries on a specific database such as Medline, WebStress provides bibliometric analysis of the corpus, which might contribute to a detailed analysis on occupational stress in order to highlight the networks of researchers and to find the main topics studied in this area. WebStress is not yet available to researchers in general. It is being further developed, and also permission needs to be obtained from the eight commercial bibliographic databases that it consults.     

AN EXPERIMENTAL TEST ON RETIREMENT DECISIONS

As part of the current debate on the reform of pension systems, this paper presents an original experimental test where subjects face three different payoff sequences with identical expected value. Two central questions are analyzed. First, whether the distribution of retirement benefits across time influences the retirement decision. And second, whether actuarially fair pension systems distort the retirement decision. The results indicate both that a lump-sum payment rather than annuity benefits is far more effective in delaying the retirement decision and that recent reforms that encourage the link between lifetime contributions and pension benefits to delay the retirement decision should take into account timing considerations. ( JEL C91, H55, J26)     

Stability of feature selection in classification issues for high-dimensional correlated data

Handling dependence or not in feature selection is still an open question in supervised classification issues where the number of covariates exceeds the number of observations. Some recent papers surprisingly show the superiority of naive Bayes approaches based on an obviously erroneous assumption of independence, whereas others recommend to infer on the dependence structure in order to decorrelate the selection statistics. In the classical linear discriminant analysis (LDA) framework, the present paper first highlights the impact of dependence in terms of instability of feature selection. A second objective is to revisit the above issue using a flexible factor modeling for the covariance. This framework introduces latent components of dependence, conditionally on which a new Bayes consistency is defined. A procedure is then proposed for the joint estimation of the expectation and variance parameters of the model. The present method is compared to recent regularized diagonal discriminant analysis approaches, assuming independence among features, and regularized LDA procedures, both in terms of classification performance and stability of feature selection. The proposed method is implemented in the R package FADA, freely available from the R repository CRAN.     

Incidence des envois de fonds: une analyse à partir du cas de saisonniers mexicains employés au Canada

À partir d'une enquête menée auprès de saisonniers mexicains au Canada, les auteurs construisent un modèle à équations simultanées reposant sur la méthode des triples moindres carrés. Ils montrent que les envois de fonds ont un effet positif sur l'investissement agricole, et donc sur le revenu agricole au Mexique. Cet effet s'étend au revenu non agricole du fait d'une diversification des activités et des investissements des migrants. Ces résultats confirment la thèse de la nouvelle économie de la migration de travail: les envois de fonds contribuent effectivement au développement économique en donnant aux petits exploitants les liquidités qui leur manquent pour investir.