1,721,642 research outputs found
The Isserlis matrix and its application to non-decomposable graphical Gaussian models.
No full textThe operations of matrix completion and Isserlis matrix construction arise in the statistical analysis of graphical Gaussian models, in both the Bayesian and frequentist approaches. In this paper we study the properties of the Isserlis matrix of the completion, , of a positive definite matrix and propose an edge set indexing notation which highlights the symmetry existing between and its Isserlis matrix. In this way well-known properties of can be exploited to give an easy proof of certain asymptotic results for decomposable graphical Gaussian models, as well as to extend such results to the non-decomposable case. In particular we consider the asymptotic variance of maximum likelihood estimators, the non-informative Jeffreys prior, the Laplace approximation to the Bayes factor, the asymptotic distribution of the maximum likelihood estimators and the asymptotic posterior distribution of the parameters in a Bayesian conjugate analysis. In dealing with distributions over non-decomposable models an extension of the hyper-Markov property to models with non-chordal graphs is required. Our proposed extension is justified by an analysis of the conditional independence structure of the sufficient statistic
High risk youth: evidence on characteristics, needs and promising interventions. (Special Issue)
No full textInduced transducer orientation during ultrasound imaging: effects on abdominal muscle thickness and bladder position
No full textThe use of ultrasound imaging (USI) by physiotherapists to assess muscle behavior in clinical settings is
increasing. However, there is relatively little evidence of whether the clinical environment is conducive to valid and
reliable measurements. Accurate USI measurements depend on maintaining a relatively stationary transducer
position, because motion may distort the image and lead to erroneous conclusions. This would seem particularly
important during dynamic studies typical of a physiotherapy assessment. What is not known is how much
transducer motion can occur before error is introduced. The aim of this study is to shed some light on this question.
Eight healthy volunteers (19 to 52 y) participated. USI images were taken of the lateral abdominal wall (LAW) and
bladder base (midline suprapubic) at various manually induced transducer orientations (approximately –10 to 10
about 3 axes of rotation), which were quantified by a digital optical motion capture system. Measurements of
transversus abdominis (TrA) thickness and bladder base position (cranial /caudal and anterior/posterior) were
calculated. Repeated measures analysis of variance was performed to determine if the measurements obtained
at the induced transducer orientations were statistically different (p,0.05) from an image corresponding to
a reference or starting transducer orientation. Motion analysis data corresponding to measurements that did
not differ from reference image measurements were summarized to provide a range of acceptable transducer
motion (relative to the pelvis) for clockwise (CW)/counter-clockwise (CCW) rotation, cranial/caudal tilting,
medial/lateral tilting and inward/outward displacement. There were no significant changes in TrA thickness
measurements if CW/CCW transducer motion was ,9 and cranial/caudal or medial/lateral transducer tilting
was ,5. Further, there were no significant changes in measurements of bladder base position if CW/CCW
transducer motion was ,10, cranial/caudal or medial/lateral transducer tilting was ,10 and 8, respectively
and inward/outward motion was ,8 mm. These findings provide guidance on acceptable amounts of transducer
motion relative to the pelvis when generating measurements of TrA thickness and bladder base position. Future
sonographic studies and clinical assessment investigating these parameters could take these findings into account
to improve imaging technique reliabilit
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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