1,720,972 research outputs found
The Analysis of Three Way Data Matrices: A Method Based on Relation Measures Between Units.
No full textThe analysis of data matrices X = { xijk } by means of factorial techniques is considered in this paper. The most relevant contributions to this subject are due to Carroll (1968), Tucker (1972) and Kroonenberg (1983), within the framework of the "Anglo-saxon school". On the other side, in the French school of "Analyse des donnees" , the works of Saporta (1975), Escoufier (19S0) and Escofier, Pages (1984) can be mentioned. Our own contribution shows that dealing with this type of data matrices implies using a "strategy of analysis" and leads to the generalization of the notion of "dimensions" of X. To this purpose the neutral term mode is utilized. This is justified by a detailed examination of the different ways statistical information is usually manipulated in order to set up the data matrices to be eventually analysed. After having provided a technical definition of the notions of "strategy", "point of view" and "common component", the different types of three-mode data matrices are illustrated. These can be classified into three different categories: compact, non compact and sparse matrices, according to the characteristics of the various two-way section of X. For each type, the structures which can be defined in the different spaces (where the elements belonging to each mode can be represented) are studied in detail, according to a given “strategy”. The results of this analysis can be summarized as follows. In the compact matrices the symmetry of analysis allows for a complete study of the three possible strategies. In particular it is shown that by means of the "inter-structure" analysis of the "trajectories" of the same element according to another mode a global analysis of X is achieved, even if we limit ourselves to only one strategy. In the non compact matrices the choice of suitable metrics for each two-way section, within a given strategy, allows for the adoption of a common space, Rj , where the inter-structure analysis of the single shapes and of the "trajectories" is made possible either by deriving "common factors" or by means of the " Escoufier’s operators" . In the sparse matrices the difficulty of componing the different two-way sections gives rise to new methodological probelms for a three-way analysis of this type of data. In fact, the only techniques available for this case cannot be included within the "strategical approach", since they are capable to analyse only two-way "marginal tables"
A note on distortions induced by truncation, with application to linear regression systems
No full textWe explore the effects of truncation on the joint distribution of the observable random variables. A general formula for the distortion induced by truncation in the least-squares coefficients is presented. The implications of our derivations are illustrated with an example
Alcune osservazioni sui modelli grafici in presenza di variabili latenti
No full textTwo generalizations of the single-factor model are considered and their relations with graphical chain models with one latent variable are discussed. Some rules for identification are given and maximum likelihood estimation is considered within the framework of mixed hierarchical interaction models. An application is described where the models are fitted with MIM
Abundance and orientation responses of the sandhopper Talitrus saltator to beach nourishment and groynes building at San Rossore natural park, Tuscany, Italy
No full textBeach nourishment and groynes building were implemented to counteract erosion in sandy beaches located at San Rossore natural park (Tuscany, Italy), near the mouth of Arno river. From 2000 to 2003, nine groynes were built along 3.6 km of coastline at intervals of ca. 400 m, and two of the eight beach segments were filled with marble gravel. Here, we analysed the effects of these beach changes on the abundance and behaviour of the amphipod Talitrus saltator, using field and laboratory observations. Sampling with pitfall traps in order to use the capture frequency as a proxy of abundance was performed bimonthly from September 2004 to January 2006, and orientation experiments were carried out in autumn (2004 and 2005), and spring and summer 2005. Physical variables (beach width, swash width, beach slope, sand penetrability, mean grain size and salinity) were also recorded. The abundance of T. saltator increased with the distance from the river mouth, towards sites with: negligible amounts of marble locally used for nourishment; higher beach width and salinity; lower slope and penetrability values; medium grain sizes, and during the spring/summer seasons. A Generalized Linear Model with a predictive power of 64.5% considered three main descriptors in the model as significant: distance from the river mouth, sand penetrability and a seasonal factor. Orientation experiments showed a highly variable behaviour among sites, depending on coastal stability: at the site stabilized by the concurrent actions of nourishment and groynes protection measures, sandhoppers were oriented to the shoreline direction by using a sun compass; alternatively, at a site situated only 2 km from the nourished sites, they showed scattered orientation. These between-site differences in orientation, described through Spherically Projected Linear Models, were consistent throughout the study period. Different responses obtained at the individual (orientation) and population (captures) levels stress the need to account for several bioindicators to characterize biotic responses to both natural and anthropogenic changes in sandy beaches. © 2007 Springer-Verlag
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
Effects of beach nourishment and groynes building on population and community descriptors of mobile arthropodofauna
No full textFor decades beach nourishment and groyne building have been used to combat sandy beach erosion, but their effects on sandy beach macrofauna are often neglected. Here, we analysed the effects of beach nourishment and groyne building on a sandy beach within the San Rossore-Migliarino-Massaciuccoli Regional Park (a natural park in Tuscany, Italy) on two different levels of organization: the abundance of the crustacean amphipod Talitrus saltator (population level) and community descriptors of the sandy beach arthropod fauna (community level), with emphasis on supralittoral species. Samples were taken bimonthly from September 2004 to January 2006 using pitfall traps. T. saltator abundance was described by generalized linear models (GLMs) and arthropodofauna community descriptors were estimated by species number, diversity indexes and ordered with multivariate ordination methods. The abundance of T. saltator in different seasons was influenced by the month of sampling during the autumn-winter season and by beach width, substrate penetrability and the "species number" biotic factor during the spring-summer season. The abundance models revealed no direct effects of beach nourishment. T. saltator was shown to be both a typifying and discriminating species, confirming its key role in the community of sandy beaches. The arthropodofauna community showed sensitivity to the substrate grain size and quality changes generated by beach nourishment, as the community composition changed at the nourished sites in line with seasonal dynamics. Human actions to stabilise the shoreline therefore emerged as a driving environmental feature, altering the beach's physical characteristics and consequently its fauna on different organizational levels: it was shown to have a direct effect on the arthropodofauna community structure and on sandhopper population abundance by determining habitat availability. © 2008 Elsevier Ltd. All rights reserved
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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