Eunjung Cho

Author directory

2026

Financial institutions must prevent personally identifiable information (PII) and adversarial instructions from entering large language models (LLMs). We present regression-aware policy maintenance for Korean financial LLM input guardrails, supported by a cost-ordered Regex–NER–LLM cascade. On a privacy-preserving controlled set of 1,000 synthetic attacks and 200 routine requests, four manual iterations reduce in-distribution attack success rate (ASR) from 8.9% to 0.3% with a 0.5% false-positive rate (FPR) on the original tuning set. On a held-out split, a policy tuned only on the tuning split achieves 0/300 attack successes and 1/60 false positives, with Wilson 95% CIs of [0, 1.26]% and [0.29, 8.86]%, respectively. For policy maintenance, an LLM generates candidate patches, while paired McNemar tests, an FPR constraint, and cumulative regression checks determine acceptance or rejection. Paired regression testing detects an intermediate regression introduced in manual Round 3, while the gate rejects all five automatically generated candidates, preventing statistically unsupported changes from entering the policy. For boundary diagnosis, the rejected fifth-round candidate yields a pre-mitigation overall FPR of 28.9% across 350 benign examples, including 150 hard negatives, revealing context-blind Regex blocking and LLM-judge over-blocking hidden by routine benign requests. These results support regression-aware policy maintenance in the controlled setting while highlighting the need for broader boundary and deployment-specific evaluation.
Natural language processing (NLP) now shapes many aspects of our world, yet its potential for positive social impact is underexplored. This paper surveys work in “NLP for Social Good" (NLP4SG) across nine domains relevant to global development and risk agendas, summarizing principal tasks and challenges. We analyze ACL Anthology trends, finding that inclusion and AI harms attract the most research, while domains such as poverty, peacebuilding, and environmental protection remain underexplored. Guided by our review, we outline opportunities for responsible and equitable NLP and conclude with a call for cross-disciplinary partnerships and human-centered approaches to ensure that future NLP technologies advance the public good.

2025

Large Language Models (LLMs) are increasingly used to generate user-tailored summaries, adapting outputs to specific stakeholders. In legal contexts, this raises important questions about motivated reasoning — how models strategically frame information to align with a stakeholder’s position within the legal system. Building on theories of legal realism and recent trends in legal practice, we investigate how LLMs respond to prompts conditioned on different legal roles (e.g., judges, prosecutors, attorneys) when summarizing judicial decisions. We introduce an evaluation framework grounded in legal fact and reasoning inclusion, also considering favorability towards stakeholders. Our results show that even when prompts include balancing instructions, models exhibit selective inclusion patterns that reflect role-consistent perspectives. These findings raise broader concerns about how similar alignment may emerge as LLMs begin to infer user roles from prior interactions or context, even without explicit role instructions. Our results underscore the need for role-aware evaluation of LLM summarization behavior in high-stakes legal settings.
Hallucination in large language models (LLMs) remains a significant challenge for their safe deployment, particularly due to its potential to spread misinformation. Most existing solutions address this challenge by focusing on aligning the models with credible sources or by improving how models communicate their confidence (or lack thereof) in their outputs. While these measures may be effective in most contexts, they may fall short in scenarios requiring more nuanced approaches, especially in situations where access to accurate data is limited or determining credible sources is challenging. In this study, we take North Korea - a country characterised by an extreme lack of reliable sources and the prevalence of sensationalist falsehoods - as a case study. We explore and evaluate how some of the best-performing multilingual LLMs and specific language-based models generate information about North Korea in three languages spoken in countries with significant geo-political interests: English (United States, United Kingdom), Korean (South Korea), and Mandarin Chinese (China). Our findings reveal significant differences, suggesting that the choice of model and language can lead to vastly different understandings of North Korea, which has important implications given the global security challenges the country poses.

2024

Large language models such as ChatGPT exhibit striking political biases. If users query them about political information, they often take a normative stance. To overcome this, we align LLMs with diverse political viewpoints from 100,000 comments written by candidates running for national parliament in Switzerland. Models aligned with this data can generate more accurate political viewpoints from Swiss parties, compared to commercial models such as ChatGPT. We also propose a procedure to generate balanced overviews summarizing multiple viewpoints using such models. The replication package contains all code and data.