Document-Level Machine Translation Quality Estimation

Assessing Machine Translation (MT) quality at document level is a challenge as metrics need to account for many linguistic phenomena on different levels. Large units of text encompass different linguistic phenomena and, as a consequence, a machine translated document can have different problems. It is hard for humans to evaluate documents regarding document-wide phenomena (e.g. coherence) as they get easily distracted by problems at other levels (e.g. grammar). Although standard automatic evaluation metrics (e.g. BLEU) are often used for this purpose, they focus on n-grams matches and often disregard document-wide information. Therefore, although such metrics are useful to compare different MT systems, they may not reflect nuances of quality in individual documents. Machine translated documents can also be evaluated according to the task they will be used for. Methods based on measuring the distance between machine translations and post-edited machine translations are widely used for task-based purposes. Another task-based method is to use reading comprehension questions about the machine translated document, as a proxy of the document quality. Quality Estimation (QE) is an evaluation approach that attempts to predict MT outputs quality, using trained Machine Learning (ML) models. This method is robust because it can consider any type of quality assessment for building the QE models. Thus far, for document-level QE, BLEU-style metrics were used as quality labels, leading to unreliable predictions, as document information is neglected. Challenges of document-level QE encompass the choice of adequate labels for the task, the use of appropriate features for the task and the study of appropriate ML models. In this thesis we focus on feature engineering, the design of quality labels and the use of ML methods for document-level QE. Our new features can be classified as document-wide (use shallow document information), discourse-aware (use information about discourse structures) and consensus-based (use other machine translations as pseudo-references). New labels are proposed in order to overcome the lack of reliable labels for document-level QE. Two different approaches are proposed: one aimed at MT for assimilation with a low requirement, and another aimed at MT for dissemination with a high quality requirement. The assimilation labels use reading comprehension questions as a proxy of document quality. The dissemination approach uses a two-stage post-editing method to derive the quality labels. Different ML techniques are also explored for the document-level QE task, including the appropriate use of regression or classification and the study of kernel combination to deal with features of different nature (e.g. handcrafted features versus consensus features). We show that, in general, QE models predicting our new labels and using our discourse-aware features are more successful than models predicting automatic evaluation metrics. Regarding ML techniques, no conclusions could be drawn, given that different models performed similarly throughout the different experiments

A Quantitative Analysis of Discourse Phenomena in Machine Translation

State-of-the-art Machine Translation (MT) systems translate documents by considering isolated sentences, disregarding information beyond sentence level. As a result, machine-translated documents often contain problems related to discourse coherence and cohesion. Recently, some initiatives in the evaluation and quality estimation of MT outputs have attempted to detect discourse problems in order to assess the quality of these machine translations. However, a quantitative analysis of discourse phenomena in MT outputs is still needed in order to better understand the phenomena and identify possible solutions or ways to improve evaluation. This paper aims to answer the following questions: What is the impact of discourse phenomena on MT quality? Can we capture and measure quantitatively any issues related to discourse in MT outputs? In order to answer these questions, we present a quantitative analysis of several discourse phenomena and correlate the resulting figures with scores from automatic translation quality evaluation metrics. We show that figures related to discourse phenomena present a higher correlation with quality scores than the baseline counts widely used for quality estimation of MT

Detecting Misinformation with LLM-Predicted Credibility Signals and Weak Supervision

Credibility signals represent a wide range of heuristics that are typically used by journalists and fact-checkers to assess the veracity of online content. Automating the task of credibility signal extraction, however, is very challenging as it requires high-accuracy signal-specific extractors to be trained, while there are currently no sufficiently large datasets annotated with all credibility signals. This paper investigates whether large language models (LLMs) can be prompted effectively with a set of 18 credibility signals to produce weak labels for each signal. We then aggregate these potentially noisy labels using weak supervision in order to predict content veracity. We demonstrate that our approach, which combines zero-shot LLM credibility signal labeling and weak supervision, outperforms state-of-the-art classifiers on two misinformation datasets without using any ground-truth labels for training. We also analyse the contribution of the individual credibility signals towards predicting content veracity, which provides new valuable insights into their role in misinformation detection

Enhancing Biomedical Lay Summarisation with External Knowledge Graphs

Previous approaches for automatic lay summarisation are exclusively reliant on the source article that, given it is written for a technical audience (e.g., researchers), is unlikely to explicitly define all technical concepts or state all of the background information that is relevant for a lay audience. We address this issue by augmenting eLife, an existing biomedical lay summarisation dataset, with article-specific knowledge graphs, each containing detailed information on relevant biomedical concepts. Using both automatic and human evaluations, we systematically investigate the effectiveness of three different approaches for incorporating knowledge graphs within lay summarisation models, with each method targeting a distinct area of the encoder-decoder model architecture. Our results confirm that integrating graph-based domain knowledge can significantly benefit lay summarisation by substantially increasing the readability of generated text and improving the explanation of technical concepts.Comment: Accepted to the EMNLP 2023 main conferenc

Improving Tokenisation by Alternative Treatment of Spaces

Tokenisation is the first step in almost all NLP tasks, and state-of-the-art transformer-based language models all use subword tokenisation algorithms to process input text. Existing algorithms have problems, often producing tokenisations of limited linguistic validity, and representing equivalent strings differently depending on their position within a word. We hypothesise that these problems hinder the ability of transformer-based models to handle complex words, and suggest that these problems are a result of allowing tokens to include spaces. We thus experiment with an alternative tokenisation approach where spaces are always treated as individual tokens. Specifically, we apply this modification to the BPE and Unigram algorithms. We find that our modified algorithms lead to improved performance on downstream NLP tasks that involve handling complex words, whilst having no detrimental effect on performance in general natural language understanding tasks. Intrinsically, we find our modified algorithms give more morphologically correct tokenisations, in particular when handling prefixes. Given the results of our experiments, we advocate for always treating spaces as individual tokens as an improved tokenisation method

Bilexical embeddings for quality estimation

© 2017 The Authors. Published by Association for Computational Linguistics. This is an open access article available under a Creative Commons licence. The published version can be accessed at the following link on the publisher’s website: http://dx.doi.org/10.18653/v1/W17-4760This work was supported by the QT21 project (H2020 No. 645452)

VaxxHesitancy: A Dataset for Studying Hesitancy Towards COVID-19 Vaccination on Twitter

Vaccine hesitancy has been a common concern, probably since vaccines were created and, with the popularisation of social media, people started to express their concerns about vaccines online alongside those posting pro- and anti-vaccine content. Predictably, since the first mentions of a COVID-19 vaccine, social media users posted about their fears and concerns or about their support and belief into the effectiveness of these rapidly developing vaccines. Identifying and understanding the reasons behind public hesitancy towards COVID-19 vaccines is important for policy markers that need to develop actions to better inform the population with the aim of increasing vaccine take-up. In the case of COVID-19, where the fast development of the vaccines was mirrored closely by growth in anti-vaxx disinformation, automatic means of detecting citizen attitudes towards vaccination became necessary. This is an important computational social sciences task that requires data analysis in order to gain in-depth understanding of the phenomena at hand. Annotated data is also necessary for training data-driven models for more nuanced analysis of attitudes towards vaccination. To this end, we created a new collection of over 3,101 tweets annotated with users' attitudes towards COVID-19 vaccination (stance). Besides, we also develop a domain-specific language model (VaxxBERT) that achieves the best predictive performance (73.0 accuracy and 69.3 F1-score) as compared to a robust set of baselines. To the best of our knowledge, these are the first dataset and model that model vaccine hesitancy as a category distinct from pro- and anti-vaccine stance.Comment: Accepted at ICWSM 202

ASSET: A Dataset for Tuning and Evaluation of Sentence Simplification Models with Multiple Rewriting Transformations

In order to simplify a sentence, human editors perform multiple rewriting transformations: they split it into several shorter sentences, paraphrase words (i.e. replacing complex words or phrases by simpler synonyms), reorder components, and/or delete information deemed unnecessary. Despite these varied range of possible text alterations, current models for automatic sentence simplification are evaluated using datasets that are focused on a single transformation, such as lexical paraphrasing or splitting. This makes it impossible to understand the ability of simplification models in more realistic settings. To alleviate this limitation, this paper introduces ASSET, a new dataset for assessing sentence simplification in English. ASSET is a crowdsourced multi-reference corpus where each simplification was produced by executing several rewriting transformations. Through quantitative and qualitative experiments, we show that simplifications in ASSET are better at capturing characteristics of simplicity when compared to other standard evaluation datasets for the task. Furthermore, we motivate the need for developing better methods for automatic evaluation using ASSET, since we show that current popular metrics may not be suitable when multiple simplification transformations are performed.Comment: Accepted to ACL 2020 (camera-ready version

A Large-Scale Comparative Study of Accurate COVID-19 Information versus Misinformation

The COVID-19 pandemic led to an infodemic where an overwhelming amount of COVID-19 related content was being disseminated at high velocity through social media. This made it challenging for citizens to differentiate between accurate and inaccurate information about COVID-19. This motivated us to carry out a comparative study of the characteristics of COVID-19 misinformation versus those of accurate COVID-19 information through a large-scale computational analysis of over 242 million tweets. The study makes comparisons alongside four key aspects: 1) the distribution of topics, 2) the live status of tweets, 3) language analysis and 4) the spreading power over time. An added contribution of this study is the creation of a COVID-19 misinformation classification dataset. Finally, we demonstrate that this new dataset helps improve misinformation classification by more than 9% based on average F1 measure