1,720,965 research outputs found
Supervised Classification for Link Prediction in Facebook Ego Networks With Anonymized Profile Information
No full textSocial networks are very dynamic objects where nodes and links are continuously added or removed. Hence, an important but challenging task is link prediction, that is, to predict the likelihood of a future association between any two nodes. We use a classification approach to perform link prediction on data retrieved from Facebook in the typical form of ego networks. In addition to the more traditional topological features, we also consider the attributes of the nodes—i.e., users’ publicly available profile information—to fully assess the similarity between nodes. We propose two new attribute-based features, validating their predictive power through an extensive comparison with natural competitors from the literature. Finally, one of the proposed features is selected when building a state-of-the-art procedure for link prediction that achieves an average AUROC of 96.59% over 85 test ego networks. Valuable insights on the interpretation of the results in the specific context of friendship recommendation in Facebook are also provided
Supervised learning with indefinite topological Kernels
No full textTopological Data Analysis (TDA) is a new branch of statistics devoted to the study of the ‘shape’ of the data. As TDA's tools are typically defined in complex spaces, kernel methods are often used to perform inferential task by implicitly mapping topological summaries, most noticeably the Persistence Diagram (PD), to vector spaces. For positive definite kernels defined on PDs, however, kernel embeddings do not fully retain the metric structure of the original space. We introduce a new exponential kernel, built on the geodesic space of PDs, and we show with simulated and real applications how it can be successfully used in regression and classification tasks, despite not being positive definite
Una proposta di Meta-Analisi basata sulla combinazione di classificatory per il problema del riconoscimento del parlatore
No full textPCA-based discrimination of partially observed functional data, with an application to AneuRisk65 data set
No full textFunctional data are usually assumed to be observed on a common domain. However, it is often the case that some portion of the functional data is missing for some statistical unit, invalidating most of the existing techniques for functional data analysis. The development of methods able to handle partially observed or incomplete functional data is currently attracting increasing interest. We here briefly review this literature. We then focus on discrimination based on principal component analysis and illustrate a few possible methods via simulation studies and an application to the AneuRisk65 data set. We show that carrying out the analysis over the full domain, where at least one of the functional data is observed, may not be the optimal choice for classification purposes
On an adaptive test of time-varying effects in Cox regression
No full textCox’s proportional hazards model is routinely used in many applied
fields, especially in bio–medical research. A common phenomenon
in medical settings is the presence of a time–dependency
in the effect of one or more explanatory variables. It is then crucial
to decide whether a covariate effect is constant, as prescribed by
the standard Cox regression model, or not. Although several proposal
appeared in literature to estimate a time depending effect in
Cox model, the problem of testing the null hypothesis of a proportional
hazard against different possible alternatives has received less
attention. The main point of the present work is to introduce a new
test for time–varying effects in the proportional hazards model having
power that adapts to the smoothness of the underlying function.
Working on the Schoenfeld residuals our procedure is an adaptation
to the present setting of a multiple testing technique introduced by
Fromont and Laurent in 2006. The results are illustrated with the
well-known Mayo liver disease data
Should I stay or should I go? Using bibliometrics to identify the international mobility of highly educated Greek manpower
No full textThis paper explores the mobility of the highly educated young Greek scholars. This is made possible through a bibliometric analysis of the affiliation countries of scholars who have published in peer reviewed journals indexed in Scopus. Approximately half of the researchers are identified from publications covered in Scopus for the period 2000–2019. A general taxonomy model is followed for analysing scientific mobility using affiliation changes. The greatest share of researchers (78.3%) appear to be static (74.6% in Greece and 3.7% abroad), whereas the mobile researcher category (21.7%) is divided into migrants (8.9%)—researchers who have left their country of origin—and travellers (12.8%)—researchers who gain additional affiliations while maintaining affiliation with their country of origin. According to the findings, the majority and especially the researcher elite (90.5%) did not sever ties with their country of origin, Greece, but instead built a chain of affiliations that linked nations together. Such chains are represented as groups of countries (clusters), in which the scientific connections between different countries can be visualised. It can be reasoned that the majority of researchers (70.3%) have a tendency to publish to a group of countries with ‘traditionally’ significant scientific impact
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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