62,723 research outputs found
Look at the First Sentence: Position Bias in Question Answering
Many extractive question answering models are trained to predict start and
end positions of answers. The choice of predicting answers as positions is
mainly due to its simplicity and effectiveness. In this study, we hypothesize
that when the distribution of the answer positions is highly skewed in the
training set (e.g., answers lie only in the k-th sentence of each passage), QA
models predicting answers as positions can learn spurious positional cues and
fail to give answers in different positions. We first illustrate this position
bias in popular extractive QA models such as BiDAF and BERT and thoroughly
examine how position bias propagates through each layer of BERT. To safely
deliver position information without position bias, we train models with
various de-biasing methods including entropy regularization and bias
ensembling. Among them, we found that using the prior distribution of answer
positions as a bias model is very effective at reducing position bias,
recovering the performance of BERT from 37.48% to 81.64% when trained on a
biased SQuAD dataset.Comment: 13 pages, EMNLP 202
Element-centric clustering comparison unifies overlaps and hierarchy
Clustering is one of the most universal approaches for understanding complex
data. A pivotal aspect of clustering analysis is quantitatively comparing
clusterings; clustering comparison is the basis for many tasks such as
clustering evaluation, consensus clustering, and tracking the temporal
evolution of clusters. In particular, the extrinsic evaluation of clustering
methods requires comparing the uncovered clusterings to planted clusterings or
known metadata. Yet, as we demonstrate, existing clustering comparison measures
have critical biases which undermine their usefulness, and no measure
accommodates both overlapping and hierarchical clusterings. Here we unify the
comparison of disjoint, overlapping, and hierarchically structured clusterings
by proposing a new element-centric framework: elements are compared based on
the relationships induced by the cluster structure, as opposed to the
traditional cluster-centric philosophy. We demonstrate that, in contrast to
standard clustering similarity measures, our framework does not suffer from
critical biases and naturally provides unique insights into how the clusterings
differ. We illustrate the strengths of our framework by revealing new insights
into the organization of clusters in two applications: the improved
classification of schizophrenia based on the overlapping and hierarchical
community structure of fMRI brain networks, and the disentanglement of various
social homophily factors in Facebook social networks. The universality of
clustering suggests far-reaching impact of our framework throughout all areas
of science
Exploring the academic invisible web
Purpose: To provide a critical review of Bergman's 2001 study on the Deep
Web. In addition, we bring a new concept into the discussion, the Academic
Invisible Web (AIW). We define the Academic Invisible Web as consisting of all
databases and collections relevant to academia but not searchable by the
general-purpose internet search engines. Indexing this part of the Invisible
Web is central to scientific search engines. We provide an overview of
approaches followed thus far. Design/methodology/approach: Discussion of
measures and calculations, estimation based on informetric laws. Literature
review on approaches for uncovering information from the Invisible Web.
Findings: Bergman's size estimate of the Invisible Web is highly questionable.
We demonstrate some major errors in the conceptual design of the Bergman paper.
A new (raw) size estimate is given. Research limitations/implications: The
precision of our estimate is limited due to a small sample size and lack of
reliable data. Practical implications: We can show that no single library alone
will be able to index the Academic Invisible Web. We suggest collaboration to
accomplish this task. Originality/value: Provides library managers and those
interested in developing academic search engines with data on the size and
attributes of the Academic Invisible Web.Comment: 13 pages, 3 figure
Bibliometrics of systematic reviews : analysis of citation rates and journal impact factors
Background:
Systematic reviews are important for informing clinical practice and health policy. The aim of this study was to examine the bibliometrics of systematic reviews and to determine the amount of variance in citations predicted by the journal impact factor (JIF) alone and combined with several other characteristics.
Methods:
We conducted a bibliometric analysis of 1,261 systematic reviews published in 2008 and the citations to them in the Scopus database from 2008 to June 2012. Potential predictors of the citation impact of the reviews were examined using descriptive, univariate and multiple regression analysis.
Results:
The mean number of citations per review over four years was 26.5 (SD +/-29.9) or 6.6 citations per review per year. The mean JIF of the journals in which the reviews were published was 4.3 (SD +/-4.2). We found that 17% of the reviews accounted for 50% of the total citations and 1.6% of the reviews were not cited. The number of authors was correlated with the number of citations (r = 0.215, P =5.16) received citations in the bottom quartile (eight or fewer), whereas 9% of reviews published in the lowest JIF quartile (<=2.06) received citations in the top quartile (34 or more). Six percent of reviews in journals with no JIF were also in the first quartile of citations.
Conclusions:
The JIF predicted over half of the variation in citations to the systematic reviews. However, the distribution of citations was markedly skewed. Some reviews in journals with low JIFs were well-cited and others in higher JIF journals received relatively few citations; hence the JIF did not accurately represent the number of citations to individual systematic reviews
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