Tom Stafford’s research while affiliated with The University of Sheffield and other places

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Publications (64)


Examples of screenshots displayed in the survey
This figure presents two screenshots of real political ads placed on Facebook.
Ad-level average acceptability rating
This figure displays the average ad-level acceptability scores for 2375 ads.
Predicted values of ad acceptability by supporter group and ad source with 95% CIs
This figure shows the predicted values of ad acceptability by supporter group (Labour vs. Conservative) and ad source (Conservative vs. non-Conservative), with 95% confidence intervals.
Reasons why people find the ads unacceptable: ad-level analysis
This figure illustrates the reasons why people find online political ads unacceptable.
What makes online political ads unacceptable? Interrogating public attitudes to inform regulatory responses
  • Article
  • Full-text available

June 2025

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10 Reads

Humanities and Social Sciences Communications

Junyan Zhu

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Tom Stafford

Online political advertising is often portrayed negatively, yet there is limited evidence regarding what exactly the public deems unacceptable. This paper provides new insights into public attitudes based on an online survey conducted in 2022, in which 1881 respondents evaluated political ads placed on Facebook during the 2019 UK General Election. We find that citizens do not inherently view political ads as unacceptable, and that perceptions of acceptability are influenced by partisan and demographic factors. We also find that ads deemed compliant with existing regulatory protocols for non-political advertising are considered more acceptable, suggesting a case for extending the existing regulatory regime to political ads. Delving deeper into our survey data, we explore the drivers behind these perceptions of acceptability and find that concerns about the content and tone of ads play a significant role. These findings provide valuable insights for those seeking to develop codes of conduct to govern practices in this space. Overall, our study offers a nuanced understanding of public attitudes toward online political advertising and identifies possible pathways for regulatory reform.

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Value-based decision-making in daily tobacco smokers following experimental manipulation of mood

May 2025

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4 Reads

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Kevin Michael King

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Background: Induction of negative mood increases tobacco choice in dependent smokers; however, less is known about the mechanisms behind this. This study addressed this gap by applying a computational model of value-based decision-making to tobacco and tobacco-unrelated choices following mood manipulation. Method: Using a pre-registered, within-subject design, 49 daily tobacco smokers (›10 daily cigarettes) watched two different videos which primed them to experience negative and positive mood (tobacco valuation and devaluation, respectively). Participants completed self-report measures of mood and craving to smoke before and after priming, followed by a two-alternative forced-choice task with (separate) blocks of tobacco-related and unrelated (animal) images. On each block, participants selected the image that they previously rated higher. A drift-diffusion model was fitted to the reaction time and error data to estimate evidence accumulation (EA) processes and response thresholds during the different blocks. Results: After watching videos intended to induce negative mood, happiness scores were lower (p ‹ .001, d = 1.16), while sadness and craving to smoke scores were higher (both ps ‹ .001, ds › .60), compared to after watching videos intended to induce positive mood. However, contrary to hypotheses, the experimental manipulation did not robustly affect EA rates (F = 1.15, p = .29, ηp2 = .02) or response thresholds (F = .07, p = .79, ηp2 = .00) for either tobacco or tobacco-unrelated decisions. Conclusions: Manipulation of mood in daily smokers did not lead to alterations in the internal processes that precede value-based decisions made about tobacco and tobacco-unrelated cues.


An Expert Guide to Planning Experimental Tasks For Evidence-Accumulation Modeling

May 2025

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100 Reads

Advances in Methods and Practices in Psychological Science

Evidence-accumulation models (EAMs) are powerful tools for making sense of human and animal decision-making behavior. EAMs have generated significant theoretical advances in psychology, behavioral economics, and cognitive neuroscience and are increasingly used as a measurement tool in clinical research and other applied settings. Obtaining valid and reliable inferences from EAMs depends on knowing how to establish a close match between model assumptions and features of the task/data to which the model is applied. However, this knowledge is rarely articulated in the EAM literature, leaving beginners to rely on the private advice of mentors and colleagues and inefficient trial-and-error learning. In this article, we provide practical guidance for designing tasks appropriate for EAMs, relating experimental manipulations to EAM parameters, planning appropriate sample sizes, and preparing data and conducting an EAM analysis. Our advice is based on prior methodological studies and the our substantial collective experience with EAMs. By encouraging good task-design practices and warning of potential pitfalls, we hope to improve the quality and trustworthiness of future EAM research and applications.


Value-based decision-making in daily tobacco smokers following experimental manipulation of mood

May 2025

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3 Reads

Background: Induction of negative mood increases tobacco choice in dependent smokers; however, less is known about the mechanisms behind this. This study addressed this gap by applying a computational model of value-based decision-making to tobacco and tobacco-unrelated choices following mood manipulation. Method: Using a pre-registered, within-subject design, 49 daily tobacco smokers (›10 daily cigarettes) watched two different videos which primed them to experience negative and positive mood (tobacco valuation and devaluation, respectively). Participants completed self-report measures of mood and craving to smoke before and after priming, followed by a two-alternative forced-choice task with (separate) blocks of tobacco-related and unrelated (animal) images. On each block, participants selected the image that they previously rated higher. A drift-diffusion model was fitted to the reaction time and error data to estimate evidence accumulation (EA) processes and response thresholds during the different blocks. Results: After watching videos intended to induce negative mood, happiness scores were lower (p ‹ .001, d = 1.16), while sadness and craving to smoke scores were higher (both ps ‹ .001, ds › .60), compared to after watching videos intended to induce positive mood. However, contrary to hypotheses, the experimental manipulation did not robustly affect EA rates (F = 1.15, p = .29, ηp2 = .02) or response thresholds (F = .07, p = .79, ηp2 = .00) for either tobacco or tobacco-unrelated decisions. Conclusions: Manipulation of mood in daily smokers did not lead to alterations in the internal processes that precede value-based decisions made about tobacco and tobacco-unrelated cues.


Value-Based Decision-Making in Daily Tobacco Smokers Following Experimental Manipulation of Mood

Induction of negative mood increases tobacco choice in dependent smokers; however, less is known about the mechanisms behind this. This study addressed this gap by applying a computational model of value-based decision making to tobacco and tobacco-unrelated choices following mood manipulation. Using a preregistered, within-subject design, 49 daily tobacco smokers (>10 daily cigarettes) watched two different videos which primed them to experience negative and positive mood (tobacco valuation and devaluation, respectively). Participants completed self-report measures of mood and craving to smoke before and after priming, followed by a two-alternative forced-choice task with (separate) blocks of tobacco-related and tobacco-unrelated (animal) images. On each block, participants selected the image that they previously rated higher. A drift-diffusion model was fitted to the reaction time and error data to estimate evidence accumulation processes and response thresholds during the different blocks. After watching videos intended to induce negative mood, happiness scores were lower (p < .001, d = 1.16), while sadness and craving to smoke scores were higher (both ps < .001, ds > .60) compared to after watching videos intended to induce positive mood. However, contrary to hypotheses, the experimental manipulation did not robustly affect evidence accumulation rates (F = 1.15, p = .29, ηp² = .02) or response thresholds (F = .07, p = .79, ηp² = .00) for either tobacco or tobacco-unrelated decisions. Manipulation of mood in daily smokers did not lead to alterations in the internal processes that precede value-based decisions made about tobacco and tobacco-unrelated cues.


Value-based decision-making in daily tobacco smokers following experimental manipulation of mood

April 2025

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5 Reads

Background: Induction of negative mood increases tobacco choice in dependent smokers; however, less is known about the mechanisms behind this. This study addressed this gap by applying a computational model of value-based decision-making to tobacco and tobacco-unrelated choices following mood manipulation. Method: Using a pre-registered, within-subject design, 49 daily tobacco smokers (›10 daily cigarettes) watched two different videos which primed them to experience negative and positive mood (tobacco valuation and devaluation, respectively). Participants completed self-report measures of mood and craving to smoke before and after priming, followed by a two-alternative forced-choice task with (separate) blocks of tobacco-related and unrelated (animal) images. On each block, participants selected the image that they previously rated higher. A drift-diffusion model was fitted to the reaction time and error data to estimate evidence accumulation (EA) processes and response thresholds during the different blocks. Results: After watching videos intended to induce negative mood, happiness scores were lower (p ‹ .001, d = 1.16), while sadness and craving to smoke scores were higher (both ps ‹ .001, ds › .60), compared to after watching videos intended to induce positive mood. However, contrary to hypotheses, the experimental manipulation did not robustly affect EA rates (F = 1.15, p = .29, ηp2 = .02) or response thresholds (F = .07, p = .79, ηp2 = .00) for either tobacco or tobacco-unrelated decisions. Conclusions: Manipulation of mood in daily smokers did not lead to alterations in the internal processes that precede value-based decisions made about tobacco and tobacco-unrelated cues.


T-test results for interaction patterns of DeepFakeDeLiBot w.r.t. group performance gain and linear regression results.
Deepfake article example. Text in blue indicates a paragraph written by LLMs.
Collaborative Evaluation of Deepfake Text with Deliberation-Enhancing Dialogue Systems

March 2025

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7 Reads

The proliferation of generative models has presented significant challenges in distinguishing authentic human-authored content from deepfake content. Collaborative human efforts, augmented by AI tools, present a promising solution. In this study, we explore the potential of DeepFakeDeLiBot, a deliberation-enhancing chatbot, to support groups in detecting deepfake text. Our findings reveal that group-based problem-solving significantly improves the accuracy of identifying machine-generated paragraphs compared to individual efforts. While engagement with DeepFakeDeLiBot does not yield substantial performance gains overall, it enhances group dynamics by fostering greater participant engagement, consensus building, and the frequency and diversity of reasoning-based utterances. Additionally, participants with higher perceived effectiveness of group collaboration exhibited performance benefits from DeepFakeDeLiBot. These findings underscore the potential of deliberative chatbots in fostering interactive and productive group dynamics while ensuring accuracy in collaborative deepfake text detection. \textit{Dataset and source code used in this study will be made publicly available upon acceptance of the manuscript.



Descriptive Statistics for Variables of Interest (Mean and SD for Quantitative Variables and Percentage and Number of Cases for Categorical Variables)
Linear Mixed-Effect Model Coefficients
Integrating Natural Language Processing to Assess the Effect of Loneliness and Social isolation on Cognitive Decline in Dementia: A Retrospective Cohort Analysis

February 2025

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22 Reads

INTRODUCTION: The study aimed to compare cognitive trajectories between patients with reports of social isolation and loneliness and those without. METHODS: Reports of social isolation, loneliness, and Montreal Cognitive Assessment (MoCA) scores were extracted from dementia patients' medical records using Natural Language Processing models and analysed using mixed-effects models. RESULTS: Lonely patients (n = 382) showed lower MoCA scores throughout the disease (B = -0.83, t = -2.64, p = 0.008). Socially isolated patients (n = 523) experienced faster cognitive decline six months before diagnosis (B = -0.21, t = -2.18, p = 0.029), but were comparable to controls (n = 3912) before this period. This led to lower MoCA scores at diagnosis (B = -0.69, t = -2.53, p = 0.011) and in later stages. DISCUSSION: Lower cognitive levels in lonely and socially isolated patients suggest that these factors may contribute to dementia progression. KEYWORDS: Social isolation, Loneliness, Electronic Health Records, Natural Language Processing, Tertiary prevention


Changes in cognition of ADRD patients: effects of social isolation proxies, utilising data from UK electronic health records

January 2025

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4 Reads

Background Marital status and living status are components of social isolation (SI), a modifiable factor thought to impact cognitive resilience, which has the potential to impact cognition throughout the course of Alzheimer’s and related dementia (ADRD) diagnosis. Electronic health records (EHRs) offer access to large scale clinical data, capable of longitudinal analyses. Method Cognitive function measurement – Montreal Cognitive Assessment (MoCA) – data, demographic (including marital and living status as SI proxies) data and ADRD diagnosis data from patients aged 50+ years from Oxford Health NHS Foundation Trust (UK) were extracted using natural language processing algorithms from EHRs dated 1995 to 2022. Longitudinal multilevel models were used to predict cognition as a function of the interaction between diagnosis duration and SI proxies, controlling for age, sex and diagnosis cause. Result ‘Lifelong single’ marital status significantly predicted reduced cognition intercept scores for the MoCA dataset (𝛽 = ‐1.61, SE = 0.67, t = ‐2.42, p = 0.016). No significant marital status predictors for slope were found. Living in supported accommodation significantly predicted steeper slopes for cognition (𝛽 = ‐2.37, SE = 0.33, t = ‐7.20, p < 0.001). No living status levels significantly predicted slopes. Conclusion Worldwide ADRD incidence is predicted to increase dramatically within the next 30 years, therefore studies investigating the impact of modifiable factors on the rates of cognitive change in ADRD patients are valuable to enhancing understanding of patient care. SI data extracted from EHRs can be used to predict differences in patient cognition scores.


Citations (25)


... Defining acceptability. The term acceptability is often referenced in research on online political advertising, yet it is rarely clearly defined in existing literature (Kozyreva et al., 2021;Dommett et al., 2024). In democratic theory, the concept of acceptability is typically grounded in frameworks emphasising core norms such as inclusiveness, effective participation, enlightened understanding and citizen control over the political agenda (Dahl, 1989), as well as the integration of care ethics into political and social structures (Held, 2006). ...

Reference:

What makes online political ads unacceptable? Interrogating public attitudes to inform regulatory responses
Understanding the communicative strategies used in online political advertising and how the public views them
  • Citing Article
  • October 2024

British Journal of Politics & International Relations

... stochastic evidence accumulation to a decision boundary (e.g., Voss et al., 2013; see Figure 1 and the related DDM glossary in Table 1). This theoretical framework has been shown not only to correlate robustly with established neural substrates (Chandrasekaran et al., 2017;Forstmann et al., 2016) but also to serve as a powerful measurement tool for examining individual differences across cognitive tasks, experimental manipulations, and participant populations (Boag et al., 2024;Donkin & Brown, 2018;Evans & Wagenmakers, 2020; but see Liu et al., 2023). Despite its theoretical contributions, the DDM is difficult to apply to experimental data in practice because the derivation of inference-relevant quantities (e.g., the likelihood function) requires a mathematical understanding of the complex stochastic process of evidence accumulation. ...

An expert guide to planning experimental tasks for evidence accumulation modelling
  • Citing Preprint
  • July 2024

... Guided by conceptual accounts (Copeland et al., 2021;Field et al., 2020), several studies have extended VBDM to addiction research (Copeland, Stafford, Acuff, et al., 2023;Copeland et al., 2024;Dora, Copeland, et al., 2023). One online experimental study (Dora, Copeland, et al., 2023) found that in heavy drinkers, inducing a negative mood altered the cognitive processes underlying value-based food decisions, but had no effect on alcohol valuation. ...

Value-based decision-making in regular alcohol consumers following experimental manipulation of alcohol value
  • Citing Article
  • May 2024

Addictive Behaviors

... Graesser et al. (2018) describes the need for team members to externalize their knowledge. Karadzhov et al. (2022) explores how deliberation may lead to team members changing their minds, which is critical for building group common ground (Stalnaker, 1978). ...

What makes you change your mind? An empirical investigation in online group decision-making conversations
  • Citing Conference Paper
  • January 2022

... This dataset comes from hugging face and contains 1 million rows with 3 columns: problem, answer and solution. See XII-E 2) Next, we use the wason card game dataset provided by [33]. This dataset contains of 500 real-world deliberation diagloues on the Wason card game problem. ...

DeliData: A Dataset for Deliberation in Multi-party Problem Solving
  • Citing Article
  • October 2023

Proceedings of the ACM on Human-Computer Interaction

... The younger generation is being increasingly exposed to the consumption of harmful substances like tobacco [4]. The use of tobacco during adolescence acts as a precursor to the adaptation of other brain-harming substances in the future [5]. Long-term effects result in a decline in the person's cognitive abilities and changes to their level of agitation [6]. ...

Recovery From Nicotine Addiction: A Diffusion Model Decomposition of Value-Based Decision-Making in Current Smokers and Ex-smokers
  • Citing Article
  • March 2023

Nicotine & Tobacco Research

... Prakannoppakun & Sinthupinyo (2016) Improved accuracy in predicting match outcomes compared to Elo Rating; specific numerical metrics not provided Semenov et al. (2017) Factorization Machines achieved the highest AUC: 0.706 for normal skill level, 0.670 for high skill level, and 0.660 for very high skill level. Shen (2022) Voting Classifier accuracy: 72.68%; individual model performances varied but were generally lower Stanlly et al. (2022) XGBoost accuracy: 93%; DT accuracy: 82%; RF accuracy: 91% Summerville et al. (2021) LSTM achieved 11.94% accuracy in hero prediction, outperforming Bayes Nets and human analysts in strict predictions Vardal et al. (2022) LSTM accuracy: 11.94%; Bayes Nets accuracy: up to 11.48% Wang et al. (2018) LR: Accuracy improved to 63.8%, SVM: Accuracy improved to 64.3% Wei et al. (2022) Win rate: 90% for Diaochan vs. Diaochan, drops when the opponent or target changes; Reward and Elo score provided in specific cases Wong et al. (2022) Accuracy: 57%-59%, precision, recall, F1-score Ye et al. (2022) Win rate: 86%-100% against various baselines, matches against top human players: AI won 7 out of 10 matches Zhang (2021) Win rate: 86%-100%, AI won 7 out of 10 matches against human Figure 5 displays the percentage distribution of different ML algorithm challenges reported by the studies. The key challenges revolve around the following issues. ...

Mind the gap: Distributed practice enhances performance in a MOBA game

... A total of 12 studies published from 2019 to 2023 were analyzed and summarized (Altay et al., 2022;Amith et al., 2019Amith et al., , 2020Brand & Stafford, 2022;EI Ayadi et al., 2022;Hong et al., 2021;Kobayashi et al., 2022Kobayashi et al., , 2023Lee et al., 2022;Luk et al., 2022;Wang et al., 2023;Weeks et al., 2023) (Appendix C). Regarding the time of the studies, two were conducted before 2020 (before the COVID-19 pandemic), and ten were conducted in 2020 or the following years (during the COVID-19 pandemic). ...

Using dialogues to increase positive attitudes towards COVID-19 vaccines in a vaccine-hesitant UK population

... Guided by conceptual accounts (Copeland et al., 2021;Field et al., 2020), several studies have extended VBDM to addiction research (Copeland, Stafford, Acuff, et al., 2023;Copeland et al., 2024;Dora, Copeland, et al., 2023). One online experimental study (Dora, Copeland, et al., 2023) found that in heavy drinkers, inducing a negative mood altered the cognitive processes underlying value-based food decisions, but had no effect on alcohol valuation. ...

Behavioral Economic and Value-Based Decision-Making Constructs That Discriminate Current Heavy Drinkers Versus People Who Reduced Their Drinking Without Treatment

... Specifically, people are able to integrate the various gains (e.g., money, self-fulfillment) and costs (e.g., time, risk, energy) of each option into a subjective value function and thus make choices according to the overall (net) value of each option. Value-based decision making has been extensively examined in behavioral, neural, and computational sciences (e.g., Apps et al., 2015;Arulpragasam et al., 2018;Copeland et al., 2022;Levy & Glimcher, 2012). ...

Methodological issues with value-based decision-making (VBDM) tasks: The effect of trial wording on evidence accumulation outputs from the EZ drift-diffusion model