Non-parametric Sampling Approximation via Voronoi Tessellations

In this article we propose a novel non-parametric sampling approach to estimate posterior distributions from parameters of interest. Starting from an initial sample over the parameter space, this method makes use of this initial information to form a geometrical structure known as Voronoi tessellation over the whole parameter space. This rough approximation to the posterior distribution provides a way to generate new points from the posterior distribution without any additional costly model evaluations. By using a traditional Markov Chain Monte Carlo (MCMC) over the non-parametric tessellation, the initial approximate distribution is refined sequentially. We applied this method to a couple of climate models to show that this hybrid scheme successfully approximates the posterior distribution of the model parameters.     

A method for K-Means seeds generation applied to text mining

In this paper, a methodology is proposed in order to produce a set of seeds later used as a starting point to K-Means-type unsupervised classification algorithms for text mining. Our proposal involves using the eigenvectors obtained from principal component analysis to extract initial seeds, upon appropriate treatment for search of lightly overlapping clusters which are also clearly identified by keywords. This work is motivated by the interest of the authors in the problem of identification of topics and themes previously unknown in short texts. Therefore, in order to validate the goodness of this method, it was applied on a sample of labeled e-mails (NG20) representing a gold standard within the field of text mining. Specifically, some corpora referenced in the literature have been used, configured in accordance to a mix of topics contained in the sample. The proposed method improves on the results of other state-of-the-art methods to which it is compared.     

Moving Ahead in Madrid: Aspirations and Expectations in the Spanish Second Generation

This paper examines determinants of aspirations and expectations among children of immigrants based on a statistically representative sample of 3,375 second generation youths interviewed in 101 public and private secondary schools in metropolitan Madrid. We review the past literature on status attainment in general and aspirations and expectations, in particular, and draw from it a set of six hypotheses to guide the analysis. Most theoretical statements in this field have been developed on the basis of U.S. data; studies in other immigrant-receiving countries, especially outside the Anglophone world, have been scarce. The study thus provides an opportunity to test and refine existing hypotheses in a different national context. We present breakdowns of educational and occupational aspirations and expectations by gender, parental education and type of school attended. This is followed by multivariate regressions of all four dependent variables on these three plus other predictors suggested by the research literature. This analysis ends with structural equation models - recursive and non-recursive - that provide an integrated theoretical statement of the causal structure of ambition in the Spanish context. Implications of our findings for theory and policy are examined. Suggestions for future research in this field are discussed.     

Reciprocal Upper Semicontinuity and Better Reply Secure Games: A Comment

A convex, compact, and possibly discontinuous better reply secure game has a Nash equilibrium. We introduce a very weak notion of continuity that can be used to establish that a game is better reply secure and we show that this notion of continuity is satisfied by a large class of games.     

Spanish adaptation of the Antifat Attitudes Scale / Adaptación al castellano de la Escala de Actitud Antiobesos

Antifat attitudes may be defined as the negative assessment of people with weight problems. To evaluate them, the Antifat Attitudes Scale (AFA) has been used in most studies. The aim of this study is to adapt the AFA questionnaire to the Spanish population. The sample was made up of 1,457 university students from all over Spain. Exploratory and confirmatory factor analyses showed that the items on the questionnaire fit a three-factor model corresponding to the three dimensions proposed by the original author (dislike, fear of fat and willpower) and that they are interrelated. In light of these results, we conclude that the questionnaire is methodologically valid and can be used by the scientific community to measure antifat attitudes.     

Understanding Undocumented Migration from Honduras

Quantitative evidence on the drivers of undocumented migration from Honduras is limited. As a result, policy responses have been reactionary and understudied. Migration flows from the country are distinct from the rest of the region and merit study. By implementing different survey instruments, including focus groups, in‐depth interviews and a nationally representative survey, we build the first nationally representative data‐set on migrant attitudes in the country. Our results show that the propensity to migrate of individuals living in low‐income households is inversely related to human capital accumulation and access to basic services. Similarly, variables linked to networks in the destination country are positively correlated with the propensity to migrate. The prevalence of violence in areas where potential migrants live is unrelated to their migration decisions. This indicates that the focus of migration policy should rest in improving material conditions.     

Maximal domains of preferences preserving strategy-proofness for generalized median voter schemes

We characterize the maximal sets of preferences under which generalized median voter schemes are strategy-proof. Those domains are defined by a qualified version of single-peakedness, which depends on the distribution of power among agents implied by each generalized median voter scheme. Received: 28 April 1997/Accepted: 30 January 1998