1,720,959 research outputs found
The burnt matchstick
No full textIn an informal study, two versions of a story involving probability are introduced to undergraduates. The findings reveal that students have troubles detecting equal probabilities in a sampling scheme without replacement in which no information on earlier draws is available
DESPOTA: an algorithm to automatically detect a reliable partition on a dendrogram
No full textThe output of hierarchical clustering methods is typically displayed as a dendrogram describing a family of nested partitions. However, the typical approach, horizontally cutting the dendrogram at a given distance level, explores only a restricted subset of the whole set of partitions. We proposed an algorithm, DESPOTA - DEndrogram Slicing through a PermutatiOn Test Approach (Bruzzese and Vistocco, 2015), exploiting the methodological framework of permutation tests (Pesarin and Salmaso, 2010), that permits a partition to be automatically found where clusters do not necessarily obey the above principle.
DESPOTA offers a validated partition to the final user and it adapts to every choice of the distance metric and agglomeration criterion used to grow the tree. The algorithm retraces the tree downward, starting from the root of the dendrogram, where all objects are classified in a unique cluster, and moving down a partial threshold until a link joining two clusters is encountered. A permutation test is then performed in order to verify whether the two clusters should be considered a single group (the null hypothesis) or not (the alternative one). If the Null cannot be rejected, the corresponding branch will become an element of the final partition and none of its sub-branches will be processed any longer. Otherwise each of them will be further visited in the course of the procedure.
DESPOTA is shown in action both on real and synthetic datasets through a comparison with competitive methods (Gurrutxaga, 2010), (Milligan, 1981) (Tibshirani, 2001). The results obtained both on synthetic and real datasets show that DESPOTA performs well in situations characterized by different data and cluster structures
Determining the authenticity of PDO buffalo mozzarella: an approach based on Fourier transform infrared (MIR-FTIR) spectroscopy and on chemometric tools
Full text linkThe potential of Mid-infrared spectroscopy coupled with chemometric tools was evaluated for the authentication and discrimination of PDO (Protected Denomination of Origin) buffalo mozzarella produced by traditional and industrial cheese-making processes.
Samples of mozzarella provided by local producers and supermarkets were analysed through both official destructive methods and Attenuated Total Reflectance-Fourier transform infrared spectroscopy (FTIR/ATR). In particular, destructive methods allowed to determine the content of fatty substances, proteins, moisture and total nitrogen.
The results show that only the conjunction of MID-infrared spectroscopy with chemometric analysis can provide a satisfying solution to discriminate between the different types of mozzarella
DESPOTA: an algorithm to detect the partition in the extended hierarchy of a dendrogram
No full textDESPOTA is a method proposed to seek the best partition among the ones hosted in a dendrogram. The algorithm visits nodes from the tree root toward the leaves. At each node, it tests the null hypothesis that the two descending branches sustain only one cluster of units through a permutation test approach. At the end of the procedure, a partition of the data into clusters is returned. This paper focuses on the interpretation of the test statistic using a data–driven approach, exploiting a real dataset to show the details of the test statistic and the algorithm in action. The working principle of DESPOTA is shown in the light of the Lance–Williams recurrence formula, which embeds all types of agglomeration methods
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
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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