1,721,284 research outputs found
Correspondence amongst microstructure patterns observed in otoacoustic emissions and Békésy audiometry
No full textStatistical methods for investigating heterogeneity related to methodological quality in meta-analyses of studies of diagnostic accuracy [Oral O28]
No full text
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
A methodological review of how heterogeneity has been examined in systematic reviews of diagnostic test accuracy
No full textBackground
Systematic reviews of therapeutic interventions are now commonplace in many if not most areas of healthcare, and in recent years interest has turned to applying similar techniques to research evaluating diagnostic tests. One of the key parts of any review is to consider how similar or different the available primary studies are and what impact any differences have on studies’ results. Between-study differences or heterogeneity in results can result from chance, from errors in calculating accuracy indices or from true heterogeneity, that is, differences in design, conduct, participants, tests and reference tests. An important additional consideration for diagnostic studies is differences in results due to variations in the chosen threshold for a positive result for either the index or reference test.Dealing with heterogeneity is particularly challenging for diagnostic test reviews, not least because test accuracy is conventionally represented by a pair of statistics and not by a single measure of effect such as relative risk, and as a result a variety of statistical methods are available that differ in the way in which they tackle the bivariate nature of test accuracy data:
methods that undertake independent analyses of each aspect of test performance methods that further summarise test performance into a single summary statistic methods that use statistical models that simultaneously consider both dimensions of test performance. The validity of a choice of meta-analytical method depends in part on the pattern of variability (heterogeneity) observed in the study results. However, currently there is no empirical guidance to judge which methods are appropriate in which circumstances, and the degree to which different methods yield comparable results. All this adds to the complexity and difficulty of undertaking systematic reviews of diagnostic test accuracy.Objectives
Our objective was to review how heterogeneity has been examined in systematic reviews of diagnostic test accuracy studies. Methods
Systematic reviews that evaluated a diagnostic or screening test by including studies that compared a test with a reference test were identified from the Centre for Reviews and Dissemination’s Database of Abstracts of Reviews of Effects. Reviews for which structured abstracts had been written up to December 2002 were screened for inclusion. Data extraction was undertaken using standardised data extraction forms by one reviewer and checked by a second.Results
A total of 189 systematic reviews met our inclusion criteria and were included in the review. The median number of studies included in the reviews was 18 [inter-quartile range (IQR) 20]. Meta-analyses (n = 133) have a higher number with a median of 22 studies (IQR 20) compared with 11 (IQR 13) for narrative reviews (n = 56).Identification of heterogeneity
Graphical plots to demonstrate the spread in study results were provided in 56% of meta-analyses; in 79% of cases these were in the form of plots of sensitivity and specificity in the receiver operating characteristic (ROC) space (commonly termed ‘ROC plots’).Statistical tests to identify heterogeneity were used in 32% of reviews: 41% of meta-analyses and 9% of reviews using narrative syntheses. The c2 test and Fisher’s exact test to assess heterogeneity in individual aspects of test performance were most commonly used. In contrast, only 16% of meta-analyses used correlation coefficients to test for a threshold effect.Type of syntheses used
A narrative synthesis was used in 30% of reviews. Of the meta-analyses, 52% carried out statistical pooling alone, 18% conducted only summary receiver operator characteristic (SROC) analyses and 30% used both methods of statistical synthesis. Of the reviews that pooled accuracy indices, most pooled each aspect of test performance separately with only a handful producing single summaries of test performance such as the diagnostic odds ratio. For those undertaking SROC analyses, the main differences between the models used were the weights chosen for the regression models. In fact, in 42% of cases (27/64) the use of, or choice of, weight was not provided by the review authors. The proportion of reviews using statistical pooling alone has declined over time from 67% in 1995 to 42% in 2001, with a corresponding increase in the use of SROC methods, from 33% to 58%. However, two-thirds of those using SROC methods also carried out statistical pooling rather than presenting only SROC models. Reviews using SROC analyses also tended to present their results as some combination of sensitivity and specificity rather than using alternative, perhaps less clinically meaningful, means of data presentation such as diagnostic odds ratios.Investigation of heterogeneity sources
Three-quarters of meta-analyses attempted to investigate statistically possible sources of variation, using subgroup analysis (76) or regression analysis (44). The median number of variables investigated was four, ranging from one variable in 20% of reviews to over six in 27% of reviews. The ratio of median number of variables to median number of studies was 1:6.The impact of clinical or socio-demographic variables was investigated in 74% of these reviews and test- or threshold-related variables in 79%. At least one quality-related variable was investigated in 63% of reviews. Within this subset, the most commonly considered variables were the use of blinding (41% of reviews), sample size (33%), the reference test used (28%) and the avoidance of verification bias (25%).Conclusions
The emphasis on pooling individual aspects of diagnostic test performance and the under-use of statistical tests and graphical approaches to identify heterogeneity perhaps reflect the uncertainty in the most appropriate methods to use and also greater familiarity with more traditional indices of test accuracy. This is an indication of the level of difficulty and complexity of carrying out these reviews. It is strongly suggested that in such reviews meta-analyses are carried out with the involvement of a statistician familiar with the field
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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