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- PublicationTweeting Europe: A text-analytic approach to unveiling the content of political actors' Twitter activities in the European ParliamentTwitter is an important platform for communication and is frequently used by Members of the European Parliament (MEPs) to campaign and en- gage in discussion with constituents and colleagues in the parliament. Ex- amining the issues that MEPs talk about on Twitter can thus inform us about their political priorities. Topic modelling aims to summarise a corpus of documents by capturing the underlying hidden structure of the data and pre- senting the user with an overview of the key subjects and themes discussed in the corpus, known as topics. This paper aims to quantify and explore the content that MEPs pay attention to on Twitter by applying a new en- semble approach for topic modelling which involves applying two layers of Non-Negative Matrix Factorisation (NMF). The resulting set of issues paid attention to by MEPs are explained by considering the effects of events, is- sue characteristics, and MEP characteristics.
- PublicationEnsemble Topic Modeling via Matrix FactorizationTopic models can provide us with an insight into the underlying latent structure of a large corpus of documents, facilitating knowledge discovery and information summarization. A range of methods have been proposed in the literature, including probabilistic topic models and techniques based on matrix factorization. However, these methods tend to have stochastic elements in their initialization, which can lead to their output being unstable. That is, if a topic modeling algorithm is applied to the same data multiple times, the output will not necessarily always be the same. With this idea of stability in mind we ask the question – how can we produce a definitive topic model that is both stable and accurate? To address this, we propose a new ensemble topic modeling method, based on Non-negative Matrix Factorization (NMF), which combines a collection of unstable topic models to produce a definitive output. We evaluate this method on an annotated tweet corpus, where we show that this new approach is more accurate and stable than traditional NMF.
- PublicationStability of topic modeling via matrix factorizationTopic models can provide us with an insight into the underlying latent structure of a large corpus of documents. A range of methodshave been proposed in the literature, including probabilistic topic models and techniques based on matrix factorization. However, inboth cases, standard implementations rely on stochastic elements in their initialization phase, which can potentially lead to differentresults being generated on the same corpus when using the same parameter values. This corresponds to the concept of instabilitywhich has previously been studied in the context of k-means clustering. In many applications of topic modeling, this problem ofinstability is not considered and topic models are treated as being definitive, even though the results may change considerably if theinitialization process is altered. In this paper we demonstrate the inherent instability of popular topic modeling approaches, usinga number of new measures to assess stability. To address this issue in the context of matrix factorization for topic modeling, wepropose the use of ensemble learning strategies. Based on experiments performed on annotated text corpora, we show that a K-Foldensemble strategy, combining both ensembles and structured initialization, can significantly reduce instability, while simultaneouslyyielding more accurate topic models
Scopus© Citations 58 347
- PublicationSynthetic Dataset Generation for Online Topic ModelingOnline topic modeling allows for the discovery of the underlying latent structure in a real time stream of data. In the evaluation of such approaches it is common that a static value for the number of topics is chosen. However, we would expect the number of topics to vary over time due to changes in the underlying structure of the data, known as concept drift and concept shift. We propose a semi-synthetic dataset generator, which can introduce concept drift and concept shift into existing annotated non-temporal datasets, via user-controlled paramaterization. This allows for the creation of multiple different artificial streams of data, where the “correct” number and composition of the topics is known at each point in time. We demonstrate how these generated datasets can be used as an evaluation strategy for online topic modeling approaches.
- PublicationEnsemble Topic Modeling using Weighted Term Co-associationsTopic modeling is a popular unsupervised technique that is used to discover the latent thematic structure in text corpora. The evaluation of topic models typically involves measuring the semantic coherence of the terms describing each topic, where a single value is used to summarize the quality of an overall model. However, this can create difficulties when one seeks to interpret the strengths and weaknesses of a given topic model. With this in mind, we propose a new ensemble topic modeling approach that incorporates both stability information, in the form of term co-associations, and semantic similarity information, as derived from a word embedding constructed on a background corpus. Our evaluations show that this approach can simultaneously yield higher quality models when considering the produced topic descriptors and document-topic assignments, while also facilitating the comparison and evaluation of solutions through the visualization of the discovered topical structure, the ordering of the topic descriptors, and the ranking of term pairs which appear in topic descriptors.
Scopus© Citations 9 127