1,720,977 research outputs found
A comparison of priors for variance parameters in Bayesian basket trials
No full textPhase II basket trials are popular tools to evaluate efficacy of a new treatment targeting genetic alteration common to a set of different cancer histologies. Efficient designs are obtained by pooling data from the different arms (e.g., cancer histologies) via Bayesian hierarchical modelling, with a variance parameter controlling the strength of shrinkage of each arm treatment effect to the overall treatment effect. One critical aspect of this approach is that prior choice on the variance plays a major role in determining the strength of shrinkage and impacts the operating characteristics of the design. We review the priors most commonly adopted in previous works and compare them with the recently introduced penalized complexity (PC) priors. Our simulation study shows comparable behaviour for the PC prior and the gold standard choice half-t prior, with the former performing better in the homogeneous scenario where all histologies respond similarly to the treatment. We argue that PC priors offer advantages over other priors because they allow the user to handle the degree of shrinkage by means of only one parameter and can be elicited based on clinical opinion when available
Is the classical Wald test always suitable under response-adaptive randomization?
Full text linkThe aim of this paper is to analyze the impact of response-adaptive randomization rules for normal response trials
intended to test the superiority of one of two available treatments. Taking into account the classical Wald test, we show
how response-adaptive methodology could induce a consistent loss of inferential precision. Then, we suggest a modified
version of theWald test which, by using the current allocation proportion to the treatments as a consistent estimator of
the target, avoids some degenerate scenarios and so it should be preferable to the classical test. Furthermore, we show
both analytically and via simulations how some target allocations may induce a locally decreasing power function. Thus,
we derive the conditions on the target guaranteeing its monotonicity and we show how a correct choice of the initial
sample size allows one to overcome this drawback regardless of the adopted target
A competitive design-based spatial predictor
Full text linkUnder the finite population design-based framework, locations' spatial information coordinates of a population have traditionally been used to develop efficient sampling designs rather than for estimation or prediction. We propose to enhance design-based individual prediction by exploiting the spatial information derived from geography, which is available for each population element before sampling. Individual predictors are obtained by reinterpreting deterministic interpolators under the finite population design-based framework, making it possible to derive their statistical properties. Monte Carlo experiments on real and simulated data help to appreciate the performances of the proposed approach in comparison both with estimators that do not employ spatial information and with kriging. We found that under the most favorable conditions for kriging, the proposed predictor shows at least the same performances, while outperforming kriging for small sample sizes
Compound optimal allocations for survival clinical trials
Full text linkThe aim of the present paper is to provide optimal allocations for comparative
clinical trials with survival outcomes. The suggested targets are derived adopting
a compound optimization strategy based on a subjective weighting of the
relative importance of inferential demands and ethical concerns. The ensuing
compound optimal targets are continuous functions of the treatment effects, so
we provide the conditions under which they can be approached by standard
response-adaptive randomization procedures, also guaranteeing the applicability
of the classical asymptotic inference. The operating characteristics of the suggested
methodology are verified both theoretically and by simulation, including
the robustness to model misspecification.With respect to the other available proposals,
our strategy always assigns more patients to the best treatment without
compromising inference, taking into account estimation efficiency and power as
well.We illustrate our procedure by redesigning two real oncological trials
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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