1,720,983 research outputs found
Bivariate meta-analysis of predictive values of diagnostic tests can be an alternative to bivariate meta-analysis of sensitivity and specificity
Full text linkOBJECTIVE: Meta-analysis of predictive values is usually discouraged because
these values are directly affected by disease prevalence, but sensitivity and
specificity sometimes show substantial heterogeneity as well. We propose a
bivariate random-effects logitnormal model for the meta-analysis of the positive
predictive value (PPV) and negative predictive value (NPV) of diagnostic tests.
STUDY DESIGN AND SETTING: Twenty-three meta-analyses of diagnostic accuracy were
reanalyzed. With separate models, we calculated summary estimates of the PPV and
NPV and summary estimates of sensitivity and specificity. We compared these
summary estimates, the goodness of fit of the two models, and the amount of
heterogeneity of both approaches.
RESULTS: There were no substantial differences in the goodness of fit or amount
of heterogeneity between both models. The median absolute difference between the
projected PPV and NPV from the summary estimates of sensitivity and specificity
and the summary estimates of PPV and NPV was 1% point (interquartile range, 0-2%
points).
CONCLUSION: A model for the meta-analysis of predictive values fitted the data
from a range of systematic reviews equally well as meta-analysis of sensitivity
and specificity. The choice for either model could be guided by considerations of
the design used in the primary studies and sources of heterogeneity
Variation of a test's sensitivity and specificity with disease prevalence
No full textBACKGROUND:Anecdotal evidence suggests that the sensitivity and specificity of a diagnostic test may vary with disease prevalence. Our objective was to investigate the associations between disease prevalence and test sensitivity and specificity using studies of diagnostic accuracy. METHODS:We used data from 23 meta-analyses, each of which included 10-39 studies (416 total). The median prevalence per review ranged from 1% to 77%. We evaluated the effects of prevalence on sensitivity and specificity using a bivariate random-effects model for each metaanalysis, with prevalence as a covariate. We estimated the overall effect of prevalence by pooling the effects using the inverse variance method. RESULTS:Within a given review, a change in prevalence from the lowest to highest value resulted in a corresponding change in sensitivity or specificity from 0 to 40 percentage points. This effect was statistically significant (p < 0.05) for either sensitivity or specificity in 8 metaanalyses (35%). Overall, specificity tended to be lower with higher disease prevalence; there was no such systematic effect for sensitivity. INTERPRETATION:The sensitivity and specificity of a test often vary with disease prevalence; this effect is likely to be the result of mechanisms, such as patient spectrum, that affect prevalence, sensitivity and specificity. Because it may be difficult to identify such mechanisms, clinicians should use prevalence as a guide when selecting studies that most closely match their situation
Use of methodological search filters to identify diagnostic accuracy studies can lead to the omission of relevant studies
No full textOBJECTIVE: To determine the usefulness of methodological filters in search
strategies for diagnostic studies in systematic reviews.
STUDY DESIGN AND SETTING: We made an inventory of existing methodological search
filters for diagnostic accuracy studies and applied them in PubMed to a reference
set derived from 27 published systematic reviews in a broad range of clinical
fields. Outcome measures were the fraction of not identified relevant studies and
the reduction in the number of studies to read.
RESULTS: We tested 12 search filters. Of the studies included in the systematic
reviews, 2%-28% did not pass the sensitive search filters, 4%-24% did not pass
the accurate filters, and 39%-42% did not pass the specific filters. Decrease in
number-needed-to-read when a search filter was used in a search strategy for a
diagnostic systematic review varied from 0% to 77%.
CONCLUSION: The use of methodological filters to identify diagnostic accuracy
studies can lead to omission of a considerable number of relevant studies that
would otherwise be included. When preparing a systematic review, it may be
preferable to avoid using methodological filters
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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