1,721,191 research outputs found
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Detecting Differential Item and Step Functioning with Rating Scale and Partial Credit Trees
Get PDFSeveral statistical procedures have been suggested for detecting
differential item functioning (DIF) and differential step
functioning (DSF) in polytomous items. However, standard
procedures are designed for the comparison of pre-specified
reference and focal groups, such as males and females.
Here, we propose a framework for the detection of DIF and DSF in
polytomous items under the rating scale and partial credit model,
that employs a model-based recursive partitioning algorithm. In contrast to existing
procedures, with this approach no pre-specification of reference
and focal groups is necessary, because they are detected in a
data-driven way. The resulting groups are characterized by
(combinations of) covariates and thus directly interpretable.
The statistical background and construction of the new procedures
are introduced along with an instructive example. Four simulation
studies illustrate and compare their statistical properties to
the well-established likelihood ratio test (LRT). While both the
LRT and the new procedures respect a given significance level,
the new procedures are in most cases equally (simple DIF groups)
or more powerful (complex DIF groups) and can also detect
DSF. The sensitivity to model misspecification is
investigated. An application example with empirical data
illustrates the practical use.
A software implementation of the new procedures is freely
available in the R system for statistical computing
Interplay between regional climate and re-oligotrophication on lake thermal structure
Get PDFLakes are a major source of water in the Alps, and both climate change and re-oligotrophication
have affected many of them during the last decades. Lake Caldonazzo (area = 5.6 km2; southern
Alps, Italy) with its 40-year dataset, can be a model system to understand the interacting forces of
these environmental drivers on the thermal structure (temperature and thickness of the epilimnion,
hypolimnion temperature, depth of the thermocline, Schmidt stability) of intermediate-size lakes.
We used solar radiation, air temperature, wind and global circulation indices as climatic indicators
and transparency, phosphorus and chlorophyll concentrations as trophic indicators. Trend patterns
and the timing of change points in climate, lake thermal structure and trophic state were linked by a
mechanistic model of interaction. Following re-oligotrophication, in Lake Caldonazzo water
transparency increased that led to greater epilimnion depth. Within this deeper layer, the incoming
heat of climate change was distributed without increasing epilimnetic temperature until restoration
was accomplished. Afterwards, however, epilimnion thickness did not further increase and
therefore could not prevent an upward shift in epilimnetic temperature. At the same time, the
hypolimnetic temperature tended to decrease probably linked to a cooling trend in winter
temperature. Thus, our study showed that in Lake Caldonazzo the hypolimnion mainly tracked
winter climate while the epilimnion tracked the interaction between climate and restoration. The
evolution of Schmidt stability, reflecting different aspects of a lake’s thermal structure, indicated
earlier and stronger stratification. This will have important repercussions on ecosystem service
Variations on the Author
Get PDF“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
Get PDFWe 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
A new method for detecting differential item functioning in the Rasch model
Get PDFDifferential item functioning (DIF) can lead to an unfair advantage or disadvantage for certain subgroups in educational and psychological testing. Therefore, a variety of statistical methods has been suggested for detecting DIF in the Rasch model. Most of these methods are designed for the comparison of pre-specified focal and reference groups, such as males and females. Latent class approaches, on the other hand, allow to detect previously unknown groups exhibiting DIF. However, this approach provides no straightforward interpretation of the groups with respect to person characteristics.
Here we propose a new method for DIF detection based on model-based recursive partitioning that can be considered as a compromise between those two extremes. With this approach it is possible to detect groups of subjects exhibiting DIF, which are not prespecified, but result from combinations of observed covariates. These groups are directly interpretable and can thus help understand the psychological sources of DIF.
The statistical background and construction of the new method is first introduced by means of an instructive example, and then applied to data from a general knowledge quiz and a teaching evaluation
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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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