1,721,066 research outputs found
A Poisson approach to the validation of failure time surrogate endpoints in individual patient data meta-analyses
No full textSurrogate endpoints are often used in clinical trials instead of well-established hard endpoints for practical convenience. The meta-analytic approach relies on two measures of surrogacy: one at the individual level and one at the trial level. In the survival data setting, a two-step model based on copulas is commonly used. We present a new approach which employs a bivariate survival model with an individual random effect shared between the two endpoints and correlated treatment-by-trial interactions. We fit this model using auxiliary mixed Poisson models. We study via simulations the operating characteristics of this mixed Poisson approach as compared to the two-step copula approach. We illustrate the application of the methods on two individual patient data meta-analyses in gastric cancer, in the advanced setting (4069 patients from 20 randomized trials) and in the adjuvant setting (3288 patients from 14 randomized trials).The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: The present work has been supported by the Institut National du Cancer (INCa), Grant SHS 2014-141, and by the Ligue Nationale Contre le Cancer. The study sponsors had no involvement in either the study design; the collection, analysis, and interpretation of data; the writing of the manuscript; nor in the decision to submit the manuscript for publication
Evaluation of failure time surrogate endpoints in individual patient data meta-analyses of randomized clinical trials. A poisson approach
No full textEvaluation of failure time surrogate endpoints in individual patient data meta-analyses of randomized clinical trials. A poisson approach
No full textJoint Modelling of a Binary and a Continuous Outcome Measured at Two Cycles to Determine the Optimal Dose
No full textThe optimal dose of targeted treatment in oncology may not be the maximal tolerated dose. Evaluating jointly toxicity and efficacy data is then desirable. We propose an adaptive dose finding approach to identify a dose based on repeated binary toxicity and continuous efficacy outcomes from the first two cycles. Probit and linear Gaussian models are used for the toxicity and efficacy at each cycle respectively. The correlation between toxicity and efficacy outcome is modelled via a latent Gaussian variable. Maximum likelihood estimators are used. Two steps in this design are defined: dose escalation with decision rules based only on toxicity observed at the first cycle; the expansion cohort with decision rules based on both repeated toxicity and efficacy outcomes by using the joint model. We perform simulation studies to assess the operating characteristics of our design. The design has good performance for different scenarios. The percentage of correct selection dose varies from 54% to 84%. There is no effect on the estimation parameters with missing data of toxicity or efficacy at cycle 2. The design then has similar performance. Using repeated toxicity and efficacy data in dose finding trials provides more reliable information to estimate the optimal dose for further trials.This project was partly funded by a grant from the Institut National du Cancer (OPTIDOSE project SHS-06)
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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