1,721,157 research outputs found
An extension of Welch's approximate t-solution to comparative bioequivalence trials
No full textWe consider the problem of proving statistically the equivalence of two treatments with normally distributed observations. The size and the power of the commonly-used test procedures which assume equality of the variances are investigated when this assumption is violated. On the one hand the preassigned level is considerably exceeded, and on the other hand the power if no treatment difference exists drops heavily for differing sample sizes. We propose an extension of Welch's approximate t-solution for the Behrens-Fisher problem in bioequivalence assessment, which is asymptotically optimal in a certain subclass of tests. The behaviour of the proposed test is investigated in various finite sample situations. The results show that the extension of Welch's approximate t-solution should be preferred for testing bioequivalence of two treatments whenever the population variances cannot be assumed equal and the sample sizes are different. Sometimes the experimenter knows which sample has the larger variance. In this case, the larger sample size should always be assigned to that group with the larger variance in order to optimize the actual level and power of the test
Comparison of two measurement methods with a gold standard as applied to 20-MHz-sonography and clinical palpation for ascertaining the thickness of pigmented skin tumours
No full textAim: This paper focuses on different statistical methods for comparing two measurement methods with an additionally available gold standard. A given data example is used as the basis of the calculations. Method: We provide a complementary statistical analysis of a study presented by Hoffmann et al. [1] on sonometric and palpatory measurements of the size of pigmented skin tumours in 681 patients. Results: For comparing two measurement methods with respect to a gold standard, several statistical parameters assessing one measurement method can be used. In addition, there are further descriptive and some inference-statistical methods available. Conclusion: If there is a suitable categorization of the measurements, the comparison of the methods should be performed using the positive predictive values and kappa coefficients as descriptive measures. Moreover, the McNemar test can be used for comparing the differential accuracy of allocation. When investigating continuous measurements, a comparison using mere correlation analyses can lead to false conclusions. Therefore, we recommend the direct analysis of the individual measurement errors by means of numerical and graphical representations. The absolute values of the measurement errors can be compared using the sign test for paired samples
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
Adaptive wavelet estimation of the diffusion coefficient under additive error measurements
Full text linkWe study nonparametric estimation of the diffusion coefficient from discrete data, when the observations are blurred by additional noise. Such issues have been developed over the last 10 years in several application fields and in particular in high frequency financial data modelling, however mainly from a parametric and semiparametric point of view. This paper addresses the nonparametric estimation of the path of the (possibly stochastic) diffusion coefficient in a relatively general setting. By developing pre-averaging techniques combined with wavelet thresholding, we construct adaptive estimators that achieve a nearly optimal rate within a large scale of smoothness constraints of Besov type. Since the diffusion coefficient is usually genuinely random, we propose a new criterion to assess the quality of estimation; we retrieve the usual minimax theory when this approach is restricted to a deterministic diffusion coefficient. In particular, we take advantage of recent results of Reiß (Ann. Statist. 39 (2011) 772–802) of asymptotic equivalence between a Gaussian diffusion with additive noise and Gaussian white noise model, in order to prove a sharp lower bound
Arthur W. Munk, A way of survival. New-York, Bookman Associates, 1954
No full textTrocmé Étienne. Arthur W. Munk, A way of survival. New-York, Bookman Associates, 1954. In: Revue d'histoire et de philosophie religieuses, 36e année n°1,1956. pp. 97-98
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