Evgenia Christoforou

dblp:57/10299 · DBLP profile ↗
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14ranked-venue papers
11as first author
6since 2021 · last 2026
0000-0003-0455-9357ORCID · verified

Domains — the database's venue-derived domains; a paper can count in several

Systems, architecture and hardware · 4 · 4 first-authorDatabases, data management, data science and information retrieval · 4 · 2 first-author · 4 since 2021Human-computer interaction and ubiquitous computing · 3 · 3 first-author · 3 since 2021Artificial intelligence and machine learning · 2 · 2 since 2021Applied, interdisciplinary, general and emerging computing · 2 · 2 first-author · 2 since 2021Graphics, computer vision, multimedia, augmented reality and games · 1 · 1 since 2021
YearPublicationVenuePosition
2026 Educating the Public in Artificial Intelligence: Insights from a Large-Scale Course
abstract
As AI technologies grow more influential in shaping modern life, there is an urgent need to make AI literacy accessible beyond academic and technical communities. This paper presents the design, delivery, and evaluation of an online AI course targeting the general public. The course combined asynchronous lectures, interactive live sessions, and reflective assignments. Of the 343 people who registered, 169 completed the program. Using validated instruments administered before and after the course, we measured changes in participants’ attitudes toward AI and their AI literacy. Our findings revealed statistically significant changes in AI literacy, specifically in awareness, usage, and evaluation constructs, as well as a rise in positive attitudes toward AI. High satisfaction scores and qualitative feedback further support the course’s effectiveness. These findings reinforce the importance of inclusive, scalable educational interventions for empowering the public to navigate AI technologies.
Maria Kasinidou, Styliani Kleanthous, Jahna Otterbacher, Evgenia Christoforou
AAAI4
2025 KeepA(n)I: Social Stereotypes in and Social Norms for Computer Vision
abstract
The KeepA(n)I platform facilitates the auditing of computer vision systems that tag images, which aid visual communication on the Web and social media, from content moderation to the development of new apps and tools. In particular, KeepA(n)I enables a broad set of stakeholders to scrutinize a process of interest that embeds an image tagger for issues of social stereotyping, while also examining the social norms that humans apply to the observed AI behaviors. KeepA(n)I’s approach, and its use of the power of the crowd, can aid the stakeholders in receiving responses to both descriptive and normative questions (i.e., which stereotyping behaviors are observed and if they are considered problematic by a given “crowd” for an intended context). We provide an overview of the platform, its key features, and a discussion via a use case on the diverse set of stakeholders that can benefit from it.
Evgenia Christoforou, Nicolas C. Nicolaou, Efstathios Stavrakis, Jahna Otterbacher
ICWSM1
2024 Generative AI in Crowdwork for Web and Social Media Research: A Survey of Workers at Three Platforms
abstract
Crowdsourcing plays an important role in Web and social media research, from data annotation, to online experiments and user surveys. With the emergence of Generative AI (GenAI), researchers are considering how models and tools such as GPT might replace crowdwork. Many have already evaluated GPT on annotation tasks. However, it is less clear how GenAI might impact other types of tasks, or to what extent crowdworkers have already incorporated it into their work processes. Thus, we asked crowdworkers directly regarding their use of GenAI, via a survey at two points in time, across three commercial platforms. We found evidence that workers' self-reported use of GenAI did not change over time, but rather, was strongly correlated to the platform in which they operate, with MTurk workers using GenAI much more often than those operating at Clickworker and Prolific. As most respondents reported that survey completion is their "usual type of task", we discuss the implication of the use of GenAI in user surveys, via specific examples of ICWSM research.
Evgenia Christoforou, Gianluca Demartini, Jahna Otterbacher
ICWSM1
2022 How Does the Crowd Impact the Model? A Tool for Raising Awareness of Social Bias in Crowdsourced Training Data
abstract
It is increasingly easy for interested parties to play a role in the development of predictive algorithms, with a range of available tools and platforms for building datasets, as well as for training and evaluating machine learning (ML) models. For this reason, it is essential to create awareness among practitioners on the ethical challenges, such as the presence of social bias in training data. We present RECANT (Raising Awareness of Social Bias in Crowdsourced Training Data), a tool that allows users to explore the behaviors of four biometric models -- predicting the gender and race, as well as the perceived attractiveness and trustworthiness, of the person depicted in an input image. These models have been trained on a crowdsourced dataset of passport-style people images, where crowd annotators described attributes of the images, and reported their own demographic characteristics. With RECANT, users can explore the correct and wrong predictions made by each model, when using different subsets of the data in training, based on annotator attributes. We present its features, along with sample exercises, as a hands-on tool for raising awareness of potential pitfalls in data practices surrounding ML.
Periklis Perikleous, Andreas Kafkalias, Zenonas Theodosiou, Pinar Barlas, Evgenia Christoforou, Jahna Otterbacher, Gianluca Demartini, Andreas Lanitis
CIKM5
2021 It's About Time: A View of Crowdsourced Data Before and During the Pandemic
abstract
Data attained through crowdsourcing have an essential role in the development of computer vision algorithms. Crowdsourced data might include reporting biases, since crowdworkers usually describe what is “worth saying” in addition to images’ content. We explore how the unprecedented events of 2020, including the unrest surrounding racial discrimination, and the COVID-19 pandemic, might be reflected in responses to an open-ended annotation task on people images, originally executed in 2018 and replicated in 2020. Analyzing themes of Identity and Health conveyed in workers’ tags, we find evidence that supports the potential for temporal sensitivity in crowdsourced data. The 2020 data exhibit more race-marking of images depicting non-Whites, as well as an increase in tags describing Weight. We relate our findings to the emerging research on crowdworkers’ moods. Furthermore, we discuss the implications of (and suggestions for) designing tasks on proprietary platforms, having demonstrated the possibility for additional, unexpected variation in crowdsourced data due to significant events.
Evgenia Christoforou, Pinar Barlas, Jahna Otterbacher
CHI1
2021 Do you see what I see? Images of the COVID-19 pandemic through the lens of Google
abstract
During times of crisis, information access is crucial. Given the opaque processes behind modern search engines, it is important to understand the extent to which the "picture" of the Covid-19 pandemic accessed by users differs. We explore variations in what users "see" concerning the pandemic through Google image search, using a two-step approach. First, we crowdsource a search task to users in four regions of Europe, asking them to help us create a photo documentary of Covid-19 by providing image search queries. Analysing the queries, we find five common themes describing information needs. Next, we study three sources of variation - users' information needs, their geo-locations and query languages - and analyse their influences on the similarity of results. We find that users see the pandemic differently depending on where they live, as evidenced by the 46% similarity across results. When users expressed a given query in different languages, there was no overlap for most of the results. Our analysis suggests that localisation plays a major role in the (dis)similarity of results, and provides evidence of the diverse "picture" of the pandemic seen through Google.
Monica Lestari Paramita, Kalia Orphanou, Evgenia Christoforou, Jahna Otterbacher, Frank Hopfgartner
Inf. Process. Manag.3
2016 Evaluating reliability techniques in the master-worker paradigm
abstract
A distributed system is considered that carries out computational tasks according to the master-worker paradigm. A master has a set of computational tasks to resolve. She assigns each task to a set of workers over the Internet, instead of computing the task locally. For each task each worker reply to the master with the task result. Since the task was not computed locally, the master can not trust the result for two main reasons: (i) workers might deliberately provide an incorrect result, (ii) the result is corrupted due to some hardware or software failure during the execution of the task. Given the above, we can model our workers as either “altruistic”, always willing to provide the correct result to each task, or “troll” that are trying to provide an incorrect result to each task. Moreover we model the failure of the worker to comply with her intended behavior, as an error probability ε. The goal of the master is to compute the correct result of all the tasks with high probability. In the literature two techniques have been used to achieve this goal: (i) “voting”, that determines the correct result of a task given multiple replies of distinct workers; (ii) “challenges”, that are tasks whose result is known and can be used to detect altruistic workers. What separates our work from the current literature is the realistic modelling of the worker's behavior and the fact that we do not restrict the task result to a binary set of answers; the domain of possible replies for a task can have multiple correct and multiple incorrect results. Given the above we evaluate the performance of the two techniques described in the literature in the scenario where ε = 0 and when ε > 0. Performance is measured in terms of: (1) time, i.e., the number of rounds performed by an algorithm for the computation of all the tasks, and (2) work, i.e., the number of total task computations performed by the workers. The case where ε = 0 is used as a best case scenario that provides the optimal time and work bounds of the problem. In the case where ε > 0 we propose two “natural” algorithms: one using a combination of both voting and challenges, and a second one using only voting. Both algorithms assume that certain system parameters are known. Since this might not always be the case we also provide an algorithm that estimates correctly these parameters with high probability.
Evgenia Christoforou, Antonio Fernández 0001, Kishori M. Konwar, Nicolas C. Nicolaou
NCA1
2014 Algorithmic Mechanisms for Reliable Master-Worker Internet-Based Computing
abstract
We consider Internet-based master-worker computations, where a master processor assigns, across the Internet, a computational task to a set of untrusted worker processors, and collects their responses. Examples of such computations are the "@homeâ' projects such as SETI. In this work, various worker behaviors are considered. Altruistic workers always return the correct result of the task, malicious workers always return an incorrect result, and rational workers act based on their self-interest. In a massive computation platform, such as the Internet, it is expected that all three type of workers coexist. Therefore, in this work, we study Internet-based master-worker computations in the presence of malicious, altruistic, and rational workers. A stochastic distribution of the workers over the three types is assumed. In addition, we consider the possibility that the communication between the master and the workers is not reliable, and that workers could be unavailable. Considering all the three types of workers renders a combination of game-theoretic and classical distributed computing approaches to the design of mechanisms for reliable Internet-based computing. Indeed, in this work, we design and analyze two algorithmic mechanisms to provide appropriate incentives to rational workers to act correctly, despite the malicious workers' actions and the unreliability of the communication. Only when necessary, the incentives are used to force the rational players to a certain equilibrium (which forces the workers to be truthful) that overcomes the attempt of the malicious workers to deceive the master. Finally, the mechanisms are analyzed in two realistic Internet-based master-worker settings, a SETI-like one and a contractor-based one, such as Amazon's mechanical turk. We also present plots that illustrate the tradeoffs between reliability and cost, under different system parameters.
Evgenia Christoforou, Antonio Fernández 0001, Chryssis Georgiou, Miguel A. Mosteiro
IEEE Trans. Computers1
2013 Reputation-Based Mechanisms for Evolutionary Master-Worker Computing
Evgenia Christoforou, Antonio Fernández 0001, Chryssis Georgiou, Miguel A. Mosteiro
OPODIS1
2013 Applying the dynamics of evolution to achieve reliability in master-worker computing
abstract
SUMMARY We consider Internet‐based master–worker task computations, such as SETI@home, where a master process sends tasks, across the Internet, to worker processes; workers execute and report back some result. However, these workers are not trustworthy, and it might be at their best interest to report incorrect results. In such master–worker computations, the behavior and the best interest of the workers might change over time. We model such computations using evolutionary dynamics, and we study the conditions under which the master can reliably obtain task results. In particular, we develop and analyze an algorithmic mechanism based on reinforcement learning to provide workers with the necessary incentives to eventually become truthful. Our analysis identifies the conditions under which truthful behavior can be ensured and bounds the expected convergence time to that behavior. The analysis is complemented with illustrative simulations. Copyright © 2013 John Wiley & Sons, Ltd.
Evgenia Christoforou, Antonio Fernández 0001, Chryssis Georgiou, Miguel A. Mosteiro
Concurr. Comput. Pract. Exp.1
2012 Achieving Reliability in Master-Worker Computing via Evolutionary Dynamics
Evgenia Christoforou, Antonio Fernández 0001, Chryssis Georgiou, Miguel A. Mosteiro
Euro-Par1
2012 Brief announcement: achieving reliability in master-worker computing via evolutionary dynamics
abstract
This work considers Internet-based task computations in which a master process assigns tasks, over the Internet, to rational workers and collect their responses. The objective is for the master to obtain the correct task outcomes. For this purpose we formulate and study the dynamics of evolution of Internet-based master-worker computations through reinforcement learning.
Evgenia Christoforou, Antonio Fernández 0001, Chryssis Georgiou, Miguel A. Mosteiro
PODC1
2011 Algorithmic Mechanisms for Internet Supercomputing under Unreliable Communication
abstract
This work, using a game-theoretic approach, considers Internet-based computations, where a master processor assigns, over the Internet, a computational task to a set of untrusted worker processors, and collects their responses. The master must obtain the correct task result, while maximizing its benefit. Building on prior work, we consider a framework where altruistic, malicious, and rational workers co-exist. In addition, we consider the possibility that the communication between the master and the workers is not reliable, and that workers could be unavailable assumptions that are very realistic for Internet-based master-worker computations. Within this framework, we design and analyze two algorithmic mechanisms that provide, when necessary, appropriate incentives to rational workers to act correctly, despite the malicious' workers actions and the unreliability of the network. These mechanisms are then applied to two realistic Internet-based master-worker settings, a SETI-like one and a contractor-based one, such as Amazon's mechanical turk.
Evgenia Christoforou, Antonio Fernández 0001, Chryssis Georgiou, Miguel A. Mosteiro
NCA1
2011 Brief Announcement: Algorithmic Mechanisms for Internet-Based Computing under Unreliable Communication
Evgenia Christoforou, Antonio Fernández 0001, Chryssis Georgiou, Miguel A. Mosteiro
DISC1